Tag Archives: screws

Security Fasteners & Tamper Proof Screws

 

Tanner Bolt & Nut Corp. features five types of security fasteners with unique drive configurations, each available in different head styles and materials. Security fasteners are cap screws, machine screws, self-drilling screws,concrete screws, sheet metal screws, nuts or bolts manufactured with a tamper proof or tamper resistant drive or head style. Installation tools are available.

The theory behind tamper-resistant fasteners is to make a fastener whose loosening requires a tool that a tamperer is unlikely to have on hand at the time of opportunity for tampering. There is no expectation that it will be impossible for a tamperer to obtain the driver. Rather, the main idea is simply that most tamperers will not bother to seek out and obtain a driver. In the cases of vandalism prevention and theft prevention, since most vandalism and theft incidents are simply crimes of easy opportunity, the idea is to “raise the bar” and make the opportunity less convenient.

A tamper proof fastener takes the theory one notch further. Some tamper proof screws require a tool that is proprietary and can only be obtained with the purchaser submitting documentation as to its intended use. Others can be installed with standard wrenches, but when tightened to a specific torque head shears off, leaving a conical, round, or flat head design that completely protects your property.

Continue reading Security Fasteners & Tamper Proof Screws

What are Hex Cap Screws?

hex-cap-screws-group

Hex Cap Screws are fasteners featuring a hexagonal, six-sided, head with a washer face on the bearing surface and a chamfered point. Commonly used in construction and machine assemblies, hex cap screws are one of the most common fasteners used on the jobsite today. Specifications for hex cap screws are described under the ASME B18.2.1-1996 standard. Hex cap screw specifications include ASTM A449 & SAE J429: Grade 2, Grade 5 & Grade 8.

Hex Cap Screws are NOT Hex Boltshex-cap-screws

Mistaking a hex cap screw for a hex bolt is a very common occurrence, but the two fasteners differ in many ways, including the way they are used and installed.

  • Hex bolts are installed by turning a nut to tighten the fastener
  • Hex cap screws are installed into tapped holes by turning the head to assemble and tighten
  • Hex cap screws feature a washer face on the bearing surface and the chamfered point
  • Hex bolts have neither the washer face or chamfered point
  • Hex cap screws are commonly used for precision applications where a tight tolerance is required
  • Hex bolts are often used in the construction industry where the mechanical properties are more important than dimensional tolerances

Grades of Hex Cap Screws

Grade 2 Hex Cap Screwshex-cap-screws3

  • Often referred to as “hardware” quality, these fasteners are typically made of low carbon steel
  • Grade 2 fasteners are ideally suited for holding wood pieces together (in combination with appropriate nuts and washers) or general hardware use where higher strength is not required
  • There is no grade marking on the head of Grade 2 fasteners
  • Many manufacturers will put a distinguishing company identification on the head

Grade 5 Hex Cap Screws

  • Tempered Grade 5 fasteners are made of medium carbon steel
  • Grade 5 fasteners are quenched and tempered for the additional strength necessary for most automotive uses and other applications where strength is a moderate concern
  • The grade marking on the head of a Grade 5 fastener is three equally-spaced lines coming out from the center of the head
  • Manufacturers’ identifications are added for traceability

Grade 8 Hex Cap Screwshex-cap-screws7

  • Tempered Grade 8 fasteners are manufactured of medium carbon alloy steel for the most demanding applications
  • Grade 8 fasteners are then quenched and tempered to superior strength and hardness qualities
  • The grade marking on a Grade 8 fastener is six equally-spaced lines coming out from the center of the head
  • Manufacturers’ identifications are added for traceability

18-8 Stainless Steel Hex Cap Screws

  • The most popular type of stainless used in the production of fasteners
  • The composition is approximately 18% chromium and 8% nickel, thus the name 18-8
  • 18-8 stainless steel consists of several grades of stainless in this classification including 302, 303, 304 and 305
  • All of these grades of 18-8 stainless steel have good strength and corrosion resistance

316 Stainless Steel Hex Cap Screwshex-cap-screws6

  • 316 stainless steel is more corrosion resistant than 18-8, but also more expensive
  • 316 stainless steel is composed of approximately 18% chromium and 12% nickel with the addition of 2% to 4% molybdenum
  • 316 stainless steel also maintains its strength at higher temperatures than 18-8

410 Stainless Steel Hex Cap Screws

  • 410 stainless steel has approximately 12% chromium with no nickel
  • 410 stainless steel is not very corrosion resistant and is magnetic, but it can be heat-treated to become harder

Additional Hex Cap Screw Technical Specification Data Available

For a more in-depth look at hex cap screws, please visit our Hex Cap Screw Technical Specification Data page.

New USA Made Self-Drilling Screws Now Available

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Avoid the Tariffs, Shop High-Quality USA Made Self-Drilling Screws

With the recent rise in tariffs, there is no better time than now to buy American made fasteners. Melted & poured in the USA, this new lineup of self-drilling screws is American through and through. Manufactured under the ISO 9001:2015 standards to be sure we consistently provide high-quality drill screws every time. These self-drilling screws are fully compliant to the Fastener Quality Act, maintaining complete lot control and traceability.

American Made Self-Drilling Screwslogo_MadeUSA

American made self-drilling screws are a staple of any construction drill screw program. Featuring TanCor Corrosion Resistant Coating, which provides 1,000 hours of salt spray protection. These self-drilling screws are heat-treated in strict accordance with SAE J78 industry standard. It is NOT recommended to use these drill screws in critical applications where dissimilar metals (aluminum) and exposure to moisture are involved. Available in a few different options:

Read on to learn more about each line of American Made Self-Drilling Screws.

New American Made Self-Drilling Screw Lineup

Standard Self-Drilling Screwbox_StandardSelfDrillingScrews_06

  • Staples of any construction job site
  • Option in with Zinc Plating (#10-16 x 3/4″)
  • All others feature TanCor Corrosion Resistant Coating
  • Provides 1000 hours of salt spray protection
  • #10, #12 & 1/4″ diameters
  • 3/4″ – 6″ lengths
  • Made in the USA

Standard Self-Drilling Screws with Bonded Sealing Washersbox_StandardSelfDrillingScrewsBW_06

  • Applications requiring a weather-tight seal
  • Galvanized bonded sealing washers
  • Option in with Zinc Plating (#10-16 x 3/4″)
  • All others feature TanCor Corrosion Resistant Coating
  • Provides 1000 hours of salt spray protection
  • #10, #12 & 1/4″ diameters
  • 3/4″ – 4″ lengths
  • Made in the USA

Heavy Duty Drilling Self-Drilling Screwsbox_HeavyDrillSelfDrillingScrews_06

  • Thick metal applications
  • For steel up to 1/2″ thick
  • Feature TanCor Corrosion Resistant Coating
  • Provides 1000 hours of salt spray protection
  • #4, #4.5 & #5 point sizes
  • #12 & 1/4″ diameters
  • 7/8″ – 6″ lengths
  • Made in the USA

Heavy Duty Drilling Self-Drilling Screws with Bonded Sealing Washersbox_HeavyDrillSelfDrillingScrewsBW_06

  • Thick metal applications (1/2″ thick steel)
  • Applications requiring a weather-tight seal
  • Galvanized Bonded Sealing Washer
  • Feature TanCor Corrosion Resistant Coating
  • Provides 1000 hours of salt spray protection
  • #4, #4.5 & #5 point sizes
  • #12 & 1/4″ diameters
  • 7/8″ – 3″ lengths
  • Made in the USA

Marine Grade 316 (A4) Stainless Steel Bi-Metal Self-Drilling Screws

EJOT® SUPER-SAPHIR JT6 Self-Drilling Screws

EJOT® SUPER-SAPHIR JT6 self-drilling screws are made from Marine Grade 316 Stainless Steel Bi-Metal. They feature a screw head and threads that are made of 316 stainless steel, providing exceptional corrosion protection and superior ductility. SUPER-SAPHIR JT6 self-drilling screws have a classic drill point and are designed to drill, form the thread and fasten components in one work step. The drill point is made of hardened carbon steel that is welded to the body. This allows JT6 fasteners to drill and tap steel up to 1/2 thick.  EJOT® SUPER-SAPHIR JT6 self-drilling screws are completed by an optional pre-assembled sealing washer.

EJOT® SUPER-SAPHIR Self-Drilling Screws Features

  • High-quality grade 316 stainless steel, ISO group A4, DIN 1.4401
  • High-quality case hardened carbon steel drill point to DIN standard 10666
  • Available with pre-assembled stainless steel EPDM vulcanized sealing washer for a safe seal every time
  • Free spin zone (near the head of the screw) for a reliable positive connection (only side lap screws)
  • Drill point with small dead center prevents misalignment on the component surface

EJOT_SuperSaphirScrewDiagramSUPER-SAPHIR JT6 Self-Drilling Screws

 

New Product Release – *Only Available at Tanner*

Proper Selection of SUPER-SAPHIR JT6 Self-Drilling Screws

To properly select your SUPER-SAPHIR JT6 Self-Drilling Screws, you must take into account the clamping thickness and required drilling performance.EJOT_ClampThicknessDiagram

Clamp Thickness

To calculate the clamp thickness, you take the thickness of the attachment (a) PLUS (+) the strength of the substructure.

The following formula can be used: Clamp Thickness Greater than or Equal to (a) + 6mm.

Drilling PerformanceEJOT_DrillingPerformanceDiagram

The drilling performance is calculated from the thickness of the components to be drilled.

The following formula can be used for Direct Bearing Surface (trapezoidal profile to steel substructure): t = component (tI) + component (tII).

The following formula can be used for Sandwich Panels: t = component (tII).

Get Increased Reliability with Sealing Washers

EJOT recommends using the sealing washers with SUPER-SAPHIR JT6 Self-Drilling Screws that are used in unweathered areas. The risk of damaging the screw joint with improper installation (excessive tightening torque, slightly sloped clamping) is significantly reduced when sealing washers are used. Clamp load and tensile stress, are also limited in the screw when using the sealing washers. The sealing washer will also help eliminate a direct exposure of the joint (protective surface coating damaged by the fastening process) – significantly dropping the risk of operational, hydrogen-induced embrittlement failure.

EJOT_SealingWasherInstallationDiagram

Correctly Install JT6 Self-Drilling Screws with Sealing Washers

When installing SUPER-SAPHIR JT6 Stainless Steel Self-Drilling Screw with Sealing Washers, depth control must be used. Adjustable depth control will prevent the deformation of the sealing washer (washer with elastomer seal). If the sealing washer is properly installed, you may see the rubber seal overlap. But if the metal back of the sealing washer changes from convex to concave, the screw was installed too tight.

slider_EJOTMarineGrade316Screws
EJOT Marine Grade 316 Stainless Steel Bi-Metal Self-Drilling Screws Available Now at Tanner

Self-Drilling Screws – How They Work

Self-Drilling Screws eliminate the need for separate drilling and tapping operations, helping provide the user with a faster, more economical installation process. Self-Drilling Screws operate on the same basic principles as a drill bit or other cutting tool. Performance for these screws are determined by cutting speed, feed rate, depth of cut and the working material being drilled into.

Optimal Performance Conditions for Self-Drilling ScrewsOptimalCuttingConditionsScrewSize

Proper installation of self-drilling screws depend on a number of factors and can (mostly) be controlled by the user. The table to the right, can be used as a guide to help properly install different nominal screw sizes. *Suggested combined maximum values. Values may be increased or decreased, as long as associated variable are changed proportionally.

  • Screw Point Geometry – the shape of the self-drilling screw drill point, not directly adjustable by the user
  • RPM – the speed of the drill/driver motor while installing the screw. Can be adjusted using a variable speed drill/driver
  • Applied Force – a measurement of the force applied by the user as the screw is installed, more force is not necessarily better
  • Work Material Hardness – the material’s resistance to drilling or cutting, in most cases, the harder the material, the more difficult it is to drill/cutSelfDrillingScrewAnatomy

Important Features to Consider When Choosing a Self-Drilling Screw

When selecting the correct self-drilling screw for your application, there are a number of factors to take into consideration. This includes the types of materials being attached and the thickness of the materials. In addition to the working material, the following design features should be also be considered before selecting your screw.

  • Drill Flutes – allow the drilled material to exit the hole, once completely embedded, the flutes can no longer remove these chips. These chips contain approximately 80% of the heat created during the installation process. If these chips buildup, this could cause the point to over-heat and fail.
  • Point Length – determines the thickness of the material which the screw can dependably drill through. The pilot section of the drill point, unthreaded portion, must be able to completely drill through the working material before the threads engage. Fasteners can bind and break if the threads engage before drilling is complete.DrillPointWings
  • Point Wings – are not present on all self-drilling screws, they are used when you need to fasten thicker materials, such as wood to metal applications. When drilled, the wings will enlarge the hole in the fastened material, allowing the threads to pass through without engaging the threads. This added clearance prevents the separation of the materials being fastened together, known as jacking. The wings will then break away once the come in contact with the metal before the threads engage the metal.

Self-Drilling Screws Available at Tanner

At Tanner we offer one of the most complete lines of self-drilling screws available. Choose from: Standard Self-Drilling Screws, Bi-Metal Self-Drilling Screws, Self-Drilling Reamers, Structural Self-Drilling Screws, Tamper-Resistant Self-Drilling Screws & much more! If you have any trouble finding a particular size or style of screw online, please feel free to reach out to one of our knowledgeable product specials – Email: websales@tannerbolt.com | Phone: 800-456-2658

Don’t Forget About

  • Screw Drill Point Material – are usually plain carbon steel which is less stable at high temperatures. To help reduce the wear on the drill point, fasten using a motor drill rather than an impact driver or hammer drill.
  • High Temperature Failure – the heat generated when drilling in self-drilling screws affects how quickly the drill point fails. For additional information on this, please refer to the troubleshooting guide below.
  • Drilling Temperature – motor RPM, applied force and work material hardness, all contribute to the the drilling temperature. Increasing any of these values also increases the heat generated.
  • Reducing Applied Force – this can help increase durability, allowing the drill point to penetrate thicker materials.
  • Reducing Motor RPM – this can help improve the performance when drilling into harder materials. This will allow the user to push harder during the drilling process and extend the drill point life.

Drill Point Failure Examples

What Screw Point is This? Understanding Screw Point Styles

Learn More About the Most Popular Screw Point Styles

In this blog post, you will learn more about the most popular Screw Point Styles on the market today. With such a wide variety of styles and variations out there, having background knowledge of each type will help you better choose the correct screw types for all of your future fastening applications. Selecting the correct screw point for your application is more important than you may think. The screw point provides a transition between the threads and the point, as well as helping with proper alignment.

Breaking Down Screw Points

To begin, we can categorize screw points into (5) major product groups, with each group having a number of different screw points available.

Screw Point Styles Explained

Tapping Screws

type a point Type A Point A thread forming screw with coarse threads and gimlet point for use in thin metal .015 to .050 thick. Used with drilled, punched or nested holes in sheet metal, resin impregnated plywood, and combinations of material.
type ab point Type AB Point A thread forming screw with spaced threads and gimlet point, combining the locating point of Type A with thread size and pitch of Type B. Normal limitations of type B apply. They are used in thin metal, resinous plywood, and various composite boards. Type AB screws offer a wider range of applications over Type A screws.
type b point Type B Point A thread forming screw with spaced threads and a blunt point with incomplete entering threads for use in heavier metal .050 to .200 thick. Larger root diameter with finer thread pitch for light and heavy sheet metal non – ferrous castings, plastics, impregnated plywood, combinations of materials, and other materials.
type bp point Type BP Point A thread forming screw with spaced threads and a cone point for use where holes are slightly misaligned. Used in heavier metal .050 to .200 thick. Larger root diameter with finer thread pitch for light and heavy sheet metal non – ferrous castings, plastics, impregnated plywood, combinations of materials, and other materials.
deckingscrew17 Type 17 Point A thread cutting screw especially for wood, with a coarse tapping screw thread and a special long sharp point fluted to capture chips. The type 17 point helps the screw penetrate quickly in some of the hardest woods.

Thread Cutting Screws

type f point Type F Point A thread cutting screw with machine screw thread with a blunt tapered point, having multi-cutting edges and chip removal cavities.For heavy gauge sheet metal, aluminum, zinc and lead die castings,cast iron, brass and plastic.
type 1 point Type 1 Point A thread cutting screw with single flute for general use. Produces a fine standard machine screw thread for field replacement. These are also known as a Type D thread cutting screws.
type 23 point Type 23 Point A thread cutting screw with fine machine screw threads, a blunt point and tapered entering edges. These screws offer maximum thread cutting area and excellent chip clearing, with minimum tightening torques. They are used in nonferrous castings, steel sheets, plastics, brass, cast iron, etc. Also known as a type T thread cutting screw.
type 25 point Type 25 Point A thread cutting screw similar to type 23 point except with coarse Type B thread. Type 25 screws have spaced, incomplete tapered threads with a blunt point and tapered entering edges, with one or more cutting edges and chip removal indentations. They are used in plastic, asbestos compositions, and other composites. These screws are also known as a type BT thread cutting screws.
type 17 point Type 17 Point A thread cutting screw for wood with a coarse tapping screw thread and a special long sharp point fluted to capture chips. Type 17 points can also be on Hi-Lo, deep root, deck screws and partical board screws.
type bf point Type BF Point Thread cutting screw with type B threads and blunt taper point having multiple cutting edges and chip cavities.
type g point Type G Point Blunt die point with a single through slot to form two cutting edges. For same general use as type C but where less driving torque is required.

Thread Forming Screws

tri-round Tri-Round: Type TT Point A thread forming screw in mostly coarse machine screw threads. It gives a further advantage of not producing chips verses a thread cutting screw in an untapped hole. Three vertexes perform a roll – forming process to form mating threads. These can be used to eliminate the tapping of unthreaded holes. Much better thread forming than Type C or CA, and drives with less torque.
type c point Type C Point A thread forming screw with either coarse or fine pitch machine screw thread and blunt tapered point. Eliminates chips and permits replacement with standard screw in the field. Higher driving torque required. Type C points are usable in heavy sheet metal and die castings.
type ca point Type CA Point A thread forming screw with either coarse or fine pitch machine screw thread. Same as Type C except with a Gimlet point. The locating point works better than Type C where holes between two adjoining pieces of sheet metal may be somewhat misaligned.
type pt thread Type PT Point A 48° or 60° thread feature reduces displacement of plastic for less internal stress and less tendency to fracture bosses. Better drive/ strip ratio and strip torque are obtained when compared with conventional Type B tapping screws. A good choice for plastic applications.
type hi-lo point Type Hi-Lo Point A Hi-Lo is a dual lead thread forming screw for use in plastic, nylon, wood, or other low density materials. The thread design reduces driving torque, improves drive to strip out torque and lessons the risk of cracking the application.
low root Low Root Point Low root thread is designed in sharp points or blunt points. The wide spaced thread forming screw is designed for plastic applications due to the increase in the drive to strip out ratio and reduced cracking of the boss.

Self-Drilling & Self-Piercing Screws

self-piercing Self-Piercing Point Produces more secure sheet metal assemblies. This fastener can be used as self-drilling screw or used to drive thru pre-punched holes or no holes in light gauge sheet metal. The twin lead drills straight thru sheet metal at peak speed. Perfectly mated threads increase strip and back out pressures. These are also know as a needle point, speed points or sprint points.
self-drilling Self-Drilling Point Comes with drilling points that will drill through metal, wood, and plastic applications. Eliminates all hole preparation, therefore reducing the in-place fastener cost. No punching, drilling or tapping required. There are several points styles including type 2, 3, 4 & 5 drill points depending on the application and size.

Machine & Tapping Screws

header point Header Point One of the least expensive pointing operations applied at the time of heading. This operation provides an end chamfer starting with a diameter smaller than the root diameter of the thread. The minimum reduction of the point is approximately 10% below the maximum minor diameter with an included angle of 40 to 50.
dog point Dog Point A straight pointed section reduced in diameter slightly below the root diameter of the thread, usually extending in length about two-thirds the diameter of the thread. Recommended for ease in starting, to insure against stripping fine threaded products, and to increase efficiency along production lines.
rolled point Rolled Point An efficient method of producing pointed long studs or long screws with an end chamfer similar to the Die Point. The last thread and a half is slightly cupped by the thread roll-over operation.
pinch point Pinch Point (Rounded) An inexpensive method of applying a 40°, 60° or 90° lead-in point having a slightly rounded contour but with pinch-off marks on its surface. Used for aligning several sheets or assembling several parts requiring pilot action.
nail point Nail Point (Pinched) Usually supplied with an approximate 45° included angle having a sharp point and slightly squared surface. Used for impinging or locking against wood or other soft material. Other degrees of included angle and sharpness also available.
cupped point Cupped Point A special cup section supplied on the end of the threaded member having a depression in the end to reduce the area in contact with the surface which increases its holding and locking power under pressure.
round point Round Point A dome-like rounded surface applied to the end of a threaded member in order to offer pressure without disfigurement. Used for adjusting members where friction without cutting action is desirable.
cone point Cone Point A precision forming operation to provide any required included angle. Offers a smooth surface, accurate length, and a sharp point which can be produced to any desired contour to fit your particular requirements.
u drive point Type U Drive Point A thread forming screw with round head metallic drive screws having multiple start threads of large helix angle, with a pivot. featuring case-hardened threads, designed to be harder than the mating part. The Type U-Drive Screw is used when an attachment is not meant to be removed. It is driven into an undersized hole for great adherence, usually in metals or plastics. U-Drive Screws also have a round, unslotted head, again intended for a permanent fixture.

Learn More About Wood, Drywall, and Masonry Screws

Masonry Screws

Masonry Screws

  •  Alternating high and low threads
  • Come in Phillips flat head or slotted hex washer head

  • Commonly blue in color

  • Self-tapping screw

  • A correctly drilled pilot hole is critical while installing masonry screws

 

Masonry screws are a self-tapping screw that can be used in a variety of base materials that include: concrete, brick, mortar joints/block and CMU. They are manufactured out of stainless or carbon steel and come with or without a corrosion coating. Masonry screws are available in two different head styles, each designed for different applications. For applications where the head needs to be countersunk in the material, a flat countersunk Phillips head screw should be used. If the screw head will be on top of the material then a hex washer head should be used.

Concrete screws have alternating high and low threads. The lead thread on the masonry screw does all the cutting of the masonry material while the screw is being installed. The lead thread will dull and hit a point where it will no longer be able to cut threads and will stop screw penetration. The abrasiveness of the masonry material will determine the exact length any specific screw can tap.

When installing masonry screws a pilot hole must be drilled with a carbide drill bit before inserting the screw. The diameter of the pilot hole is critical and must be drilled in accordance with the manufacturer’s instructions. The size of the pilot hole must be correct or it could cause the screw to break on insertion, will strip the hole, or will not provide the rated holding force.

Wood ScrewsWood Screws

  • Pre-drilling is recommended especially when using hardwoods

  • Tapered, partially threaded shank, shorter lengths are fully threaded

  • Sharp gimlet point for easy startup

  • Coarse and sharply crested threads, creates its own internal mating threads

  • Creates a tight joint, but can be removed easily without damage

 

Wood screws have a sharp gimlet point and a tapered partially threaded shaft, shorter lengths are fully threaded. Wood screws are commonly available with flat, pan, or oval heads. The unthreaded portion of the shank is designed to slip through the top board and prevent cross-threading as it pulls the two pieces of wood together.

Wood screws have coarse, sharply crested threads that create their own internal mating threads. Thread styles can greatly differ, especially in-depth and spacing. Coarse (large) threads are made for use in softwoods. While fine (smaller, closely spaced) threads work best in hardwoods. Extra coarse threads are designed for use in particleboard. High-low threads are typically found on general-purpose screws and work well with most types of wood. Serrated threads have “teeth” that help cut into the wood and make it easier to drive.

Drywall ScrewsDrywall Screws

  •  Drywall screws may be used to fasten drywall to both wood and metal studs
  • Drywall screws feature a bugle shaped Phillips head

  • The diameter of drywall screw threads is larger than the shaft diameter

  • A versatile construction fastener with many uses

 

Drywall screws have a bugle shaped Phillips head and a sharp piercing tip designed to attach drywall to wood and metal studs, while not damaging the drywall in the process. When finished driving, drywall screws are recessed slightly into the drywall. Drywall screws are typically manufactured out of case hardened steel with a black phosphate finish.

Drywall screws with coarse threads are used to attach drywall to wood framing. While drywall screws with a fine thread are best suited for attaching drywall to light-gauge steel framing. Self-drilling drywall screws are also used when working with metal studs or frames.

 

3 Common Screw Types at a Glance – Machine, Sheet Metal, and Cap Screws

Machine ScrewsMachine Screws

  •  Fully threaded shank
  • Usually used with a nut

  • Typically smaller than the average screw

  • Designed to be fastened to an existing tapped hole

Machine screws, also sometimes referred to as machine bolts, are normally smaller than the average screw. They usually range in sizes up to ¾ of an inch (19.05 mm), but can still come in larger variations. Typically machine screws are designed to be fastened to an existing tapped hole on a metal surface, usually in conjunction with a corresponding nut. The main differentiating characteristics of machine screws are: overall size, shape of head, slot type, length, material, and thread type.

The two main drive types associated with machine screws are slotted (flat head) and Phillips. There are also a number of specialized drives that they can come in, these are typically associated with tamper-resistant screws. Some of these drive types include, torx – six pointed, spanner, and trident to name a few. The shape of the head will determine how the machine screw lies once it’s fastened in place. Round and Pan heads will protrude from a flat surface, while flat head machine screws are designed for holes that are countersunk so that they lay flush with the surface.

Machine screws are always threaded the entire length of its shank. Threading on a machine screw is very important because the corresponding holes that they are being fastened into are typically tapped for a specific size and type of screw thread. The two main characteristics of threads are size of the outer diameter of the threads and pitch, the distance between each thread. Machine screw can be made to have either clockwise (right-handed) or counter-clockwise (left-handed) thread.

Sheet Metal ScrewsSheet Metal Screws

  • Fully threaded shank

  • Very versatile fastener, can be used in metal, wood, and plastics

  • Most are self-tapping screws and only require a pre-drilled hole, some come with self-drilling tips

  • Specially hardened, sharp threads that allow it to cut into material and form its own internal thread

Sheet metal screws have a fully threaded shank with sharp threads and tip that allow them to cut through metal, wood, plastic, and various other materials. The size of sheet metal screws are commonly shown as a series of three numbers, these numbers represent the diameter, thread count, and length of fastener. A sheet metal screw listed as 4-32 x 1-½” has a diameter size of 4, 32 threads per inch, and a length of 1-½”.

There are two basic types of sheet metal screws, self-tapping screws and self-drilling screws. Self-tapping screws have a sharp tip that is designed to cut through metal, but the metal must be pre-drilled before these screws can be used. Self-drilling screws have a drill point tip that can easily cut through metal without a pre-drilled hole.

The head of sheet metal screws can come in a number of different styles. Pan or round head screw will have heads that extend above the surface of the material after being installed. Flat or oval countersunk screws will be flush with the top of the material after being installed. These screws can come with a Phillips, flat, or combo drive.

Sheet metal screws made out of carbon steel are the most common and typically the most economical. These screws are prone to rust and corrosion when exposed to moisture or chemicals, so they should typically only be used indoors. Galvanized or stainless steel screws are designed to resist rust and corrosion, but tend to cost more than the standard steel screws. Sheet metal screws may be coated with zinc or nickel to modify their appearance.

Cap ScrewsCap Screws

  • Normally used without a nut

  • Available in both English and metric sizes

  • Fasten machine parts – home appliances / consumer electronic devices

  • Large head, diameter is larger than threaded portion

Cap screws have a large head and a cylindrical shaft with external threads. The head has a larger diameter than the threaded portion, this provides a positive mechanical stop when tightening the screw. Cap screws are tightened directly into a threaded or tapped hole, usually without a nut. A cap screw can generate a high amount of clamping force when tightened.

Commonly used cap screw heads styles include: hex head, socket head, and button head. Cap screws are typically  manufactured out of carbon steel, stainless steel, and metal alloys. The choice of type and size of of cap screw for a particular application mostly depends on the forces required to adequately secure the mechanical connection.

How do I Choose the Correct Self-Drilling and Self-Tapping Screws??

Self-Drilling Screws

Self-Drilling Screws operate on the same principles as drill bits and other cutting tools. This means that the way in which these screws are used affects their performance as much how they are designed.

Two important factors to consider when selecting a self-drilling screw are, material thickness and types of materials to be joined.

Screw Suitability
Optimal Cutting Parameters by Screw Size

 

 

 

 

 

 

Key Design Features to Consider when Selecting a Suitable Self-Drilling Fastener

  • Drill Flute

    • The length of the drill flute determines the metal thickness that can be drilled. Drill flutes allow the drilled material to exit the hole. If the drill flute becomes completely embedded in the material, the drill chips will clog the flute and cause the cutting action to cease. If this occurs, the heat from the drill chips could cause the drill point to become over-heated and fail.

  • Point Length

    • The drill point is the unthreaded section from the drill point to the first thread. This length must be long enough to completely drill through the material before the threads engage. If the threads engage too early, they can cause the fastener to bind and break.

  • Screw Wings

    • It is necessary to use fasteners with wings when fastening wood, over ½” thick, to metal. The wings will ream a clearance hole and keep the threads from engaging too early. If the threads engage too early, this could cause a separation of the fastened material from the base material (jacking). Once the wings hit the metal material, they will break off allowing the threads to engage.

 

Self-Tapping Screws

Self-tapping screws can tap its own hole as it is being driven into it. They can come with a sharp, piercing tip or a flat, blunt tip. Sharp tipped self-tapping screws are designed for drilling their own hole in soft materials. The flat tipped self-tapping screws will need a pilot hole drilled before being installed. Some self-tapping screws are also self-drilling screws. These screws have a drill-like flute tip that looks like the tip of a center drill, along with the tap-like flute in the leading threads. These screws are very efficient in hard substrate applications.

How the Self-Tapping Ability is Created

  • Hard Substrates – Metal or Hard Plastics

    • Often created by cutting a gap in the continuity of the thread on the screw, this generates a flute and cutting edge similar to those on a tap.

  • Soft Substrates – Wood or Soft Plastics

    • The self-tapping ability can come simply from a tip that tapers to a gimlet point (no flute is needed), the point forms the hole by displacement of the surrounding material rather than any chip forming drilling/cutting/evacuating action.