8 Types of Cap Screws and Their Applications

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8 Types of Cap Screws and Their Applications

Cap screws are fasteners that feature either internal or external socket drive heads, with different shapes depending on the type. Below the head, they have a fully or partially threaded shaft with a beveled end. These fasteners are commonly used in machinery, automotive, and industrial manufacturing due to their high yield strength and durability.

Table of contents

  • Different Types of Cap Screws and Their Applications
  • Mechanical Properties and Grades of Socket Head Cap Screws
  • ASTM Standards of Cap Screws
  • Socket Cap Screw Sizes as per ASME B18.3
  • Hexagon Socket Head Screws Size Chart (BS 2470)
  • Button Head Cap Screws Dimension
  • Recommended Tightening Torque for Button Head Screws
  • Advantages of Using Cap Screws in Machine Parts and Clamping
  • How To Measure An Allen Head Socket Cap Bolt
  • Shank and Thread Length Measurements for Allen Head Cap Bolts
  • Torque Specs For Socket Head Cap Screws
  • Cap Screw Applications
  • Knurled Head Cap Screws Certification
  • Cap Screws Metric DIN and ISO Standards
  • Cap Screws vs Socket Screws
  • Manufacturing Process of Socket Head Cap Screws

Different Types of Cap Screws and Their Applications

Type of Cap Screw Head Shape Drive Type Application
Flat Head Cap Screws flat head cap screw Countersunk Hex or Socket Used where a flush surface is needed, such as in countersunk holes
Hex Head Cap Screws Hex head cap screws Hexagonal Hex or Socket Heavy machinery and structural applications
Socket Head Cap Screws Socket head cap screws Cylindrical Hex Socket Precision applications where space is limited
Button Head Cap Screws Button head cap screws Rounded Hex or Socket Where a low profile is needed or for aesthetic purposes
Pan Head Cap Screws Pan head cap screw Rounded with a flat underside Hex or Socket General-purpose use where a large bearing surface is required
Slotted Hex Cap Screws Slotted Hex Cap Screw Hexagonal Slotted or Hex Applications where a slotted screwdriver is preferred
Torx Cap Screws Torx Cap Screw Star-shaped Torx High-torque applications
Low Head Socket Cap Screws Low Head Socket Cap Screw Low-profile cylindrical Hex Socket For applications with limited vertical space
Hex Flange Cap Screws Hex Flange Cap Screw Hexagonal with a flange Hex or Socket Automotive and machinery applications
Tri-Wing Cap Screws Tri-Wing Cap Screw Triangular winged Tri-Wing Security applications

Flat head cap screws are manufactured according to ISO 4762 standard

Mechanical Properties and Grades of Socket Head Cap Screws

Grade Strength Tensile Strength (MPa) Yield Strength (MPa) Equivalent SAE Grade
8.8 Medium strength 800 640 5
10.9 High Strength 1000 900 8
12.9 Very High Strength 1200 1080 9

ASTM Standards of Cap Screws

  • ASTM F835 (Alloy Steel Flat Countersunk and Socket Button Head Cap)
  • ASTM F912M (Alloy Steel Socket Set Screws (Metric))
  • ASTM F912 (Alloy Steel Socket Set Screws)
  • ASTM F837M (SS Socket Head Cap Screws (Metric))
  • ASTM F837 (SS Socket Head Cap Screws)

Round socket head screws are available in a wide range of sizes

Also known as round head cap screws or circle head screws, these fasteners are extremely useful in various applications. They are often used in electronics, construction, carpentry, and fastening thin materials. Due to their unique shape, they offer a secure and durable connection, making them ideal for many industrial and mechanical uses.

They are also known for their toughness and can be used as security fasteners. Without the proper tools, it can be difficult to install or remove them. In construction, they are cost-effective and provide good value for money. In carpentry, they are easy to use and suitable for woodworking projects.

Socket Cap Screw Sizes as per ASME B18.3

Round socket head screws

Thread Size 0 1 2 3 4 5 6 8 10 01/4 5/16 03/8 7/16 01/2 05/8 03/4 07/8 1
T.P.I UNF 80 72 64 56 48 44 40 36 32 28 24 24 20 20 18 16 14 12
T.P.I UNC   64 56 48 40 40 32 32 24 20 18 16 14 13 11 10 9 8
Head Dia (Max) A 0.096 0.118 0.14 0.161 0.183 0.205 0.226 0.27 0.312 0.375 0.469 0.562 0.656 0.75 0.938 1.125 1.312 1.5
Key Engagement (Min) T 0.025 0.031 0.038 0.044 0.051 0.057 0.064 0.077 0.09 0.12 0.151 0.182 0.213 0.245 0.307 0.37 0.432 0.495
Head Height (Max) H 0.06 0.073 0.086 0.099 0.112 0.125 0.138 0.164 0.19 0.25 0.312 0.375 0.438 0.5 0.625 0.75 0.875 1
Key Size J 0.05 1/16 5/64 5/64 3/32 3/32 7/64 9/64 5/32 3/16 01/4 5/16 03/8 03/8 01/2 05/8 03/4 03/4
Thread Length (Max) 0.62 0.77 0.8 0.83 0.99 1 1.05 1.19 1.27 1.5 1.71 1.94 2.17 2.38 2.82 3.25 3.69 4.12
Thread Length (Min) 0.5 0.62 0.62 0.62 0.75 0.75 0.75 0.88 0.88 1 1.12 1.25 1.38 1.5 1.75 2 2.25 2.5

Hexagon Socket Head Screws Size Chart (BS 2470)

Hexagon Socket Head Screws

Nominal size and thread dia d   0 2 1 3 5 4 6 10 8 12 5/165/16 1/41/4 3/83/8 43467 43593 7/167/16 43528 43654 43528 1 1.1/4 1.1/8 1.3/8 1.3/4 1.1/2 2
Head dia dk max.max. 0.096 0.14 0.118 0.161 0.205 0.183 0.226 5/165/16 0.27 0.343 7/167/16 3/83/8 9/169/16 43528 0.812 5/85/8 43654 1.1/8 1 1.5/16 1.75 1.5 1.875 2.5 2 2.75
min.min. 0.093 0.136 0.114 0.157 0.2 0.178 0.221 0.306 0.265 0.332 0.429 0.367 0.553 0.739 0.795 0.615 0.863 1.111 0.987 1.297            
Pitch of thread UNC — 56 64 48 40 40 32 24 32 24 18 20 16 13 12 14 11 9 10 8 7 7 6 5 6 4.1/2
UNF 8000% 6400% 7200% 5600% 4400% 4800% 4000% 3200% 3600% 2800% 2400% 2800% 2400% 2000% 1800% 2000% 1800% 1400% 1600% 14-Dec 1200% 1200% 1200% – 1200.00% –
Thread length b min.min. 0.5 0.625 0.625 0.625 0.75 0.75 0.75 0.875 0.875 0.875 1.125 1 1.25 1.5 1.625 1.375 1.75 2.25 2 2.5          
Dia of unthreaded shank dw max.max. 0.6 0.086 0.073 0.099 0.125 0.112 0.138 0.19 0.164 0.216 0.3125 0.25 0.375 0.5 0.5625 0.4375 0.625 0.875 0.75 1 1.25 1.125 1.375 1.75 1.5 2
min.min. 0.0568 0.0822 0.0695 0.0949 0.1202 0.1075 0.1329 0.184 0.1585 0.21 0.3053 0.2435 0.3678 0.4919 0.554 0.4294 0.6163 0.8647 0.7406 0.98861 1.2336 1.1086 1.3568 1.7295 1.4818 1.978
Width across flats s nom.nom. 0.05 1/161/16 0.05 5/645/64 3/323/32 5/645/64 3/323/32 5/325/32 1/81/8 5/325/32 7/327/32 3/163/16 5/165/16 43532 43532 5/165/16 43467 43724 43724 43593 43528 43528 43528 1.1/4 1 1.3/8
Thickness of head k max.max. 0.06 0.086 0.073 0.099 0.125 0.112 0.138 0.19 0.164 0.216 5/165/16 1/41/4 3/83/8 43467 0.562 7/167/16 43593 43654 43528 1 1.25 1.125 1.375 1.75 1.5 2
min.min. 0.057 0.083 0.07 0.095 0.121 0.108 0.134 0.185 0.159 0.201 0.306 0.233 0.368 0.492 0.553 0.43 0.616 0.864 0.74 0.988 1.236 1.111 1.36 1.734 1.485 1.983
Radius under head r max.max. 0.007 0.008 0.007 0.008 0.01 0.009 0.01 0.014 0.012 0.014 0.017 0.014 0.02 0.026 0.03 0.023 0.032 0.044 0.039 0.05            
min.min. 0.003 0.004 0.003 0.004 0.006 0.005 0.006 0.009 0.007 0.009 0.012 0.009 0.015 0.02 0.022 0.018 0.024 0.034 0.03 0.04            
Wall thickness w min.min. 0.019 0.028 0.023 0.032 0.04 0.036 0.044 0.061 0.052 0.074 0.1 0.08 0.12 0.16 0.18 0.14 0.2 0.28 0.24 0.32 0.475 0.428 0.523 0.665 0.57 0.76
Hex socket depth t min.min. 0.025 0.038 0.031 0.044 0.057 0.051 0.064 0.09 0.077 0.11 0.151 0.12 0.182 0.245 0.276 0.213 0.307 0.432 0.37 0.495 0.62 0.557 0.682 0.87 0.745 0.995

Check dimensions and tensile strength of button head cap screws

It has the similar shape of a pan head with the driver of a socket head. It is manufactured for fastening applications, it doesn’t have strength like standard socket screws. The socket driver is perfect for low withdrawal applications which needs a large area of clamping face.

Moreover, the button heads socket drive gives higher strength than a standard phillips which gives fitting in tight area. It has low domed head with a broader bearing surface heads, which offers a finished look. It is ideal choice when accurate appearance is required.

Button Head Cap Screws Dimension

Button Head Cap Screws

Nom thread size   M3 M4 M5 M6 M8 M10 M12 *M16
pitch   0.5 0.7 0.8 1 1,285 1.5 1.75 2
max A 5.7 7.6 9.5 10.5 14 18 21 28
max H 1.

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