8 Types of Cap Screws and Their Applications

8 Types of Cap Screws and Their Applications

A cap screws usually features internal and external socket drive heads with different shapes relying upon the type. Below the cap screw head a fully or partially threaded shaft with a bevel end. It is primarily used for machinery, automotive and industrial manufacturing applications because it offers 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
  • Recommanded Tightning 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 Bolt Lengths
  • 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 Socket Head Cap Screws

Different Types of Cap Screws and Their Applications

Types of cap screw   Head shape Drive types Application
Flat head cap screws flat head cap screw Countersunk Hex or Socket Used in applications requiring flush surfaces, countersunk holes
Hex head cap screws Hex head cap screws Hexagonal Hex or Socket heavy machinery, 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 lower profile is needed, aesthetic purposes
Pan head cap screw Pan head cap screw Rounded with a flat underside Hex or Socket General-purpose, where a large bearing surface is needed
Slotted Hex Cap Screw Slotted Hex Cap Screw Hexagonal Slotted or Hex where the ability to adjust with a slotted screwdriver is desired
Torx Cap Screw Torx Cap Screw Star-shaped Torx high-torque applications
Low Head Socket Cap Screw Low Head Socket Cap Screw Low-profile cylindrical Hex Socket For applications with limited vertical space
Hex Flange Cap Screw Hex Flange Cap Screw Hexagonal with a flange Hex or Socket automotive and machinery applications
Tri-Wing Cap Screw Tri-Wing Cap Screw Triangular winged Tri-Wing Security applications

Flat head cap screws are manufactured as per 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 wide range of sizes

It also known as round head cap screws and a circle head screws. It is extremely usually useful form of fasteners which serves many different advantages. Below given are few areas where it is used in.

It is used mostly to put electronics element together. It is very high in toughness and be used as security fasteners as well. Without the usage of accurate tools, it can be difficult to install and un-install.

Construction: It is been easily available, cost-effective, value for money material, it is often used for common construction purpose.

Carpentry: It is easy to use, tough, and not too hard to drill, it is often used for woodworking.

Fastening thin material: Due to its unique shape and it has nearly flat tops, it is ideal for fastening thin material to other kinds of material.

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 43724 7/167/16 43593 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 has 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 1.65 2.2 2.75 3.3 4.4 5.5 6.6 8.6
min T 1.05 1.35 1.92 2.08 2.75 3.35 4.16 5.2
ref S 0.35 0.35 0.45 0.45 0.45 0.6 0.6 0.6
ref R 2.95 4.1 5.2 5.6 7.5 10 11 15
nom J 2 2.5 3 4 5 6 8 10

Recommanded Tightning Torque for Button Head Screws

Unplated N-m 1.4 3.4 6.8 11 28 55 95
lbf in 12 30 60 97 248 486 840
Plated N-m 1.1 2.6 5.1 8.3 21 41 71
lbf in 9 22 45 73 186 363 630
Tensile Load KN 5.28 9.22 14.9 21.1 38.4 60.9 88.5
Socket Head Cap Screws are commonly used in machine parts and clamping

It is accurate for applications where there is not sufficient area to move or twist sockets. It is even known as socket head bolts. Due to its high clamping force, easy installation and guarded appearance, it is usually used for aerospace, automotive, construction, electronics and medical industries.

Advantages of Using Cap Screws in Machine Parts and Clamping

Available in ISO, DIN, ANSI standards for compatibility

Advantages  
Corrosion Resistance
  • excellent resistance to corrosion and rust
  • suitable for harsh environments
Precise Torque Control
  • Reducing the risk of over-tightening the fasteners
High Torque Capability
  • handle higher torque compared to other fasteners
  • secure and stable connection
Strong Load-Bearing Capacity
  • capable of handling significant loads and stresses
Low Profile Design
  • ideal for use in confined or hard-to-reach spaces
Versatility
  • suitable for a wide range of applications and machinery
Tool Compatibility
  • compatible with standard hex keys
  • commonly available and easy to use
Ease of Access
  • better access in tight spaces compared to traditional hex head bolts
Allen head cap screws are available in fine and course threads

Its fine threads and course threads gives several advantages for different application purpose. Its smaller pitches, which offers more threads per inches gives better bending strength and gives more accurate repairs. It makes it ideal for applications where quick assembly and disassembly is done, mainly in softer items like wood or plastic.

How To Measure An Allen Head Socket Cap Bolt

  • Measure Outer dia by using calipers or a micrometer
  • Measure Length from the bottom of the bolt head to the end of the bolt
  • Use a set of Allen keys to find the matching size for the socket
  • Thread pitch: measure the distance between threads
Allen Head Socket Cap Bolt

Shank and Thread Length Measurements for Allen Head Cap Bolt Lengths

Bolt Length  1-1/2" 2" 2-1/2" 3" 3-1/2" 4" 4-1/2" 5" 5-1/2"
Thread Length  1-1/2"  1-1/2"  1-1/2"  1-3/8"   1-3/8"   1-5/8"  1-5/8"   1-5/8"   1-5/8"
Shank  0"  1/2"  1"  1-5/8"  2-1/8"  2-3/8"  2-7/8"  3-3/8"  3-7/8"
Bolt Length  6" 6-1/2" 7" 7-1/2" 8" 9" 10" 11" 12"
Thread Length  1-5/8"  1-5/8"  1-5/8"   1-5/8"   1-5/8"  1-1/4" 1-1/4" 1-1/4" 1-1/4"
Shank  4-3/8"  4-7/8"  5-3/8"  5-7/8"  6-3/8"  7-3/4"  8-3/4"  9-3/4"  10-3/4"

Torque Specs For Socket Head Cap Screws

Size #0 #2 #1 #3 #5 #4 #6 #10 #8 1/4" 5/16" 7/16" 3/8" 1/2" 5/8" 7/8" 9/16" 3/4" 1-1/4" 1 1-1/2"
Socket Cap Screw UNC Nm 0.86 0.52 1.25 3 1.81 3 9 6 23 48 136 84 204 385 936 287 680 2829 1414 4930
lb ft 0.63 0.38 0.92 2 1.33 2.5 6.58 4.58 17 35 100 62 150 283 688 211 500 2080 1040 3625
UNF Nm 0.3 0.91 0.54 1.36 2.72 2.04 3.85 10.2 6.57 26 52 148 95 234 431 1043 325 764 3142 1469 5549
lb ft 0.22 0.67 0.4 1 2 1.5 2.83 7.5 4.83 19 38 109 70 172 317 767 239 562 2310 1080 4080
Button Head UNC Nm 0.52 0.29 0.8 1.4 0.9 1.81 5.1 3.4 11 23 39 97 193
lb ft 0.38 0.21 0.58 1 0.67 1.33 3.75 2.5 8 17 29 71 142
UNF Nm 0.18 0.52 0.29 0.79 1.36 1.02 2 5 3 12 24 45 113 204
lb ft 0.13 0.38 0.21 0.58 1 0.75 1 4 3 9 18 33 83 150
Flat Head (Countersunk) UNC Nm 0.52 0.29 0.79 1.36 0.91 1.7 4.53 3.4 11 23 64 39 97 193 567 136 340 1541 907
lb ft 0.38 0.21 0.58 1 0.67 1.25 3.33 2.5 8 17 47 29 71 142 417 100 250 1133 667
UNF Nm 0.18 0.52 0.29 0.79 1.47 0.91 1.93 5.1 3.51 12 24 71 45 113 215 612 154 363
lb ft 0.13 0.38 0.21 0.58 1.08 0.67 1.42 3.75 2.58 9 18 52 33 83 158 450 113 267
Grub Screws UNC Nm 0.109 0.2 0.2 0.6 1.1 0.6 1.1 4 2 10 19 49 33 71 139 408 71 272 1088 567 1282
lb ft 0.08 0.15 0.15 0.42 0.83 0.42 0.83 3 2 7 14 36 24 52 102 300 52 200 800 417 943
Low Head Cap
Screws		 UNC Nm 1.07 0.57 1.07 3.79 2.2 9 18 49 31 69 150
lb ft 0.79 0.42 0.79 2.79 1.62 6 13 36 23 51 110
Shoulder Screws UNC Nm 6 14 30 53 131 227
lb ft 4 10 22 39 96 167

Cap Screw Applications

  • Construction
  • Automotive
  • Electronics
  • Aerospace
  • Industrial machinery
Cap Screw Applications
Knurled Head Cap Screws

Knurled Head Cap Screws Certification

  • ISO9001:2015
  • AS9100D
  • Non Destructive Testing

Cap Screws Metric DIN and ISO Standards

  • DIN 912 (Socket Head Cap)
  • DIN 916 (Socket set screw)
  • DIN 7991 (Flat Head Socket Cap)
  • ISO 7380 (Button head Socket Cap)
  • DIN 7984 (Low head Socket Cap)
Cap Screws

Cap Screws vs Socket Screws

Features Cap Screws Socket Screws
Head type large, flat head with a hexagonal indentation on top cylindrical head with a hexagonal socket (Allen socket)
Thread Type full threads partial threads
Common Applications
  • construction
  • industrial
  • machinery
  • automotive
  • aerospace
  • automotive
  • electronics
  • machinery
Materials steel, stainless steel, brass etc steel, stainless steel, brass, etc
Drive types Hexagon / Square Allen
Strength high strength and durability high torque strength
Cost Less expensive more expensive due to precision machining and specific drive design

Manufacturing Process Socket Head Cap Screws

Socket Head Cap Screws

  • Material selection: stainless steel, alloy and superalloy
  • Cold Forming: shaped at room temperature
  • high-pressure technique
  • Thread Cutting or Rolling
  • Heat Treatment
  • Finishing

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