Socket Head Cap Screws
The workhorse of machine parts, die fixturing, and clamping.
Standard socket head cap screws in alloy and stainless, imperial and metric, to ASME B18.3.
Specifications & technical data.
We manufacture and stock hex socket head cap screws across the full spread of head styles, thread sizes and materials. The table below carries the complete ASME B18.3-2012 dimensions from #0 through 4″ — and when the job calls for a nonstandard size, coating or configuration, we machine it to order.
Download our hex socket head cap screw dimensioning table (PDF)
| Nominal Size (Basic Screw Diameter) | D | A | H | C | J | T | G | K | ||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Body Diameter | Head Diameter | Head Height | Max. Chamfer or Radius | Nominal Hexagon Socket Size | Minimum Key Engagement | Minimum Wall Thickness | Max. Chamfer or Radius | |||||
| Max. | Min. | Max. | Min. | Max. | Min. | |||||||
| #0 | 0.0600 | 0.0568 | 0.096 | 0.091 | 0.060 | 0.057 | 0.004 | – | 0.050 | 0.025 | 0.020 | 0.007 |
| #1 | 0.0730 | 0.0695 | 0.118 | 0.112 | 0.073 | 0.070 | 0.005 | 1/16 | 0.062 | 0.031 | 0.025 | 0.007 |
| #2 | 0.0860 | 0.0822 | 0.140 | 0.134 | 0.086 | 0.083 | 0.008 | 5/64 | 0.078 | 0.038 | 0.029 | 0.007 |
| #3 | 0.0990 | 0.0949 | 0.161 | 0.154 | 0.099 | 0.095 | 0.008 | 5/64 | 0.078 | 0.044 | 0.034 | 0.007 |
| #4 | 0.1120 | 0.1075 | 0.183 | 0.176 | 0.112 | 0.108 | 0.009 | 3/32 | 0.094 | 0.051 | 0.038 | 0.008 |
| #5 | 0.1250 | 0.1202 | 0.205 | 0.198 | 0.125 | 0.121 | 0.012 | 3/32 | 0.094 | 0.057 | 0.043 | 0.008 |
| #6 | 0.1380 | 0.1329 | 0.226 | 0.216 | 0.138 | 0.134 | 0.013 | 7/64 | 0.109 | 0.064 | 0.047 | 0.008 |
| #8 | 0.1640 | 0.1585 | 0.270 | 0.257 | 0.164 | 0.159 | 0.014 | 9/64 | 0.141 | 0.077 | 0.056 | 0.008 |
| #10 | 0.1900 | 0.1840 | 0.312 | 0.298 | 0.190 | 0.185 | 0.018 | 5/32 | 0.156 | 0.090 | 0.065 | 0.008 |
| #12 | 0.2160 | 0.2095 | 0.324 | 0.314 | 0.216 | 0.210 | 0.022 | 5/32 | 0.156 | 0.103 | 0.082 | 0.010 |
| 1/4" | 0.2500 | 0.2435 | 0.375 | 0.354 | 0.250 | 0.244 | 0.025 | 3/16 | 0.188 | 0.120 | 0.095 | 0.010 |
| 5/16" | 0.3125 | 0.3053 | 0.469 | 0.446 | 0.312 | 0.306 | 0.033 | 1/4 | 0.250 | 0.151 | 0.119 | 0.010 |
| 3/8" | 0.3750 | 0.3678 | 0.562 | 0.540 | 0.375 | 0.368 | 0.040 | 5/16 | 0.312 | 0.182 | 0.143 | 0.010 |
| 7/16" | 0.4375 | 0.4294 | 0.656 | 0.631 | 0.438 | 0.430 | 0.047 | 3/8 | 0.375 | 0.213 | 0.166 | 0.015 |
| 1/2" | 0.5000 | 0.4919 | 0.750 | 0.725 | 0.500 | 0.492 | 0.055 | 3/8 | 0.375 | 0.245 | 0.190 | 0.015 |
| 9/16" | 0.5625 | 0.5538 | 0.843 | 0.827 | 0.562 | 0.554 | 0.062 | 7/16 | 0.437 | 0.276 | 0.214 | 0.015 |
| 5/8" | 0.6250 | 0.6163 | 0.938 | 0.914 | 0.625 | 0.616 | 0.070 | 1/2 | 0.500 | 0.307 | 0.238 | 0.015 |
| 3/4" | 0.7500 | 0.7406 | 1.125 | 1.094 | 0.750 | 0.740 | 0.085 | 5/8 | 0.625 | 0.370 | 0.285 | 0.015 |
| 7/8" | 0.8750 | 0.8647 | 1.312 | 1.291 | 0.875 | 0.864 | 0.100 | 3/4 | 0.750 | 0.432 | 0.333 | 0.020 |
| 1" | 1.0000 | 0.9886 | 1.500 | 1.476 | 1.000 | 0.988 | 0.114 | 3/4 | 0.750 | 0.495 | 0.380 | 0.020 |
| 1-1/8" | 1.1250 | 1.1086 | 1.688 | 1.665 | 1.125 | 1.111 | 0.129 | 7/8 | 0.875 | 0.557 | 0.428 | 0.020 |
| 1-1/4" | 1.2500 | 1.2336 | 1.875 | 1.852 | 1.250 | 1.236 | 0.144 | 7/8 | 0.875 | 0.620 | 0.475 | 0.020 |
| 1-3/8" | 1.3750 | 1.3568 | 2.062 | 2.038 | 1.375 | 1.360 | 0.160 | 1 | 1.000 | 0.682 | 0.523 | 0.020 |
| 1-1/2" | 1.5000 | 1.4818 | 2.250 | 2.224 | 1.500 | 1.485 | 0.176 | 1 | 1.000 | 0.745 | 0.570 | 0.020 |
| 1-3/4" | 1.7500 | 1.7295 | 2.625 | 2.597 | 1.750 | 1.734 | 0.207 | 1-1/4 | 1.250 | 0.870 | 0.665 | 0.020 |
| 2" | 2.0000 | 1.9780 | 3.000 | 2.970 | 2.000 | 1.983 | 0.238 | 1-1/2 | 1.500 | 0.995 | 0.760 | 0.020 |
| 2-1/4" | 2.2500 | 2.2280 | 3.375 | 3.344 | 2.250 | 2.232 | 0.269 | 1-3/4 | 1.750 | 1.120 | 0.855 | 0.036 |
| 2-1/2" | 2.5000 | 2.4762 | 3.750 | 3.717 | 2.500 | 2.481 | 0.300 | 1-3/4 | 1.750 | 1.245 | 0.950 | 0.036 |
| 2-3/4" | 2.7500 | 2.7262 | 4.125 | 4.090 | 2.750 | 2.730 | 0.332 | 2 | 2.000 | 1.370 | 1.045 | 0.036 |
| 3" | 3.0000 | 2.9762 | 4.500 | 4.464 | 3.000 | 2.979 | 0.363 | 2-1/4 | 2.250 | 1.495 | 1.140 | 0.036 |
| 3-1/4" | 3.2500 | 3.2262 | 4.875 | 4.837 | 3.250 | 3.228 | 0.394 | 2-1/4 | 2.250 | 1.620 | 1.235 | 0.036 |
| 3-1/2" | 3.5000 | 3.4762 | 5.250 | 5.211 | 3.500 | 3.478 | 0.426 | 2-3/4 | 2.750 | 1.745 | 1.330 | 0.036 |
| 3-3/4" | 3.7500 | 3.7262 | 5.625 | 5.584 | 3.750 | 3.727 | 0.458 | 2-3/4 | 2.750 | 1.870 | 1.425 | 0.036 |
| 4" | 4.0000 | 3.9762 | 6.000 | 5.958 | 4.000 | 3.976 | 0.489 | 3 | 3.000 | 1.995 | 1.520 | 0.036 |
All dimensions in inches, per ASME B18.3-2012 — confirm requirements with our estimating team.
Standards.
What are socket screws?
Socket screws are fasteners driven from the inside. Instead of an external hex for a wrench, the head carries a recessed hexagon that takes an Allen key or hex bit — so the fastener installs down inside a counterbore, sits flush with the surface, and works in clusters too tight for a socket to swing.
- Internal hex drive — no external wrench clearance needed
- Cylindrical head that seats flush in a counterbore
- Fully or partially threaded shanks
- High clamping force from a small head footprint
- Precise, repeatable fit in machined assemblies
Common types
The socket family covers a handful of head styles, each solving a different clearance or seating problem:
- Socket Head Cap Screws — the standard, full-height head
- Low Head Cap Screws — reduced head height for shallow counterbores
- Flat (Countersunk) Cap Screws — 82° head finishes flush
- Button Cap Screws — low-profile domed head
- Socket Head Shoulder Screws — precision-ground shoulder as a bearing or pivot
- Socket Set Screws — headless, threaded end to end
- Vented Socket Screws — through-drilled for vacuum and clean service
What are socket head cap screws?
Socket head cap screws are the standard of the family: a cylindrical head whose height equals the nominal thread diameter, a head diameter of roughly one and a half times the thread, and a deep hex socket. That geometry lets a small fastener carry serious preload — which is why they run machine tools, dies, fixtures and skid packages everywhere.
We manufacture and stock them to ASME B18.3 in alloy steel per ASTM A574 as standard, and machine them to order in stainless and high-nickel alloys when the service demands it — imperial and metric, fully or partially threaded, plain or coated.
Other names
- Allen bolts / Allen screws
- Allen head cap screws
- Hex socket head cap screws
- SHCS
- Socket caps
Industries & applications
Socket head cap screws earn their keep wherever preload matters and space is short:
Oil & Gas
- Applications: valve bonnets, actuator housings, manifold and instrumentation assemblies
- Materials: A574 alloy, A193 B7 / A320 L7, 17-4 PH, super duplex
Power Generation
- Applications: turbine auxiliaries, pump and compressor packages, skid fabrication
- Materials: A193 B16, A453 660, Inconel 718
Military & Marine
- Applications: shipboard machinery, subsea tooling, defense hardware with full traceability
- Materials: Monel 400 / K500, 316L, Nitronic 50
Tips for purchasing
- Check the head against your counterbore — head diameter and height are in the table above; leave room to get the key in.
- Match the material to the service — temperature, pressure and corrosion drive the grade; our estimating team will steer you.
- Specify the thread completely — series (UNC / UNF / 8UN or metric), class of fit, and full or partial thread.
- Name the finish — black alloy is standard; PTFE-coated, zinc plated and passivated stainless are available.
- Say what paperwork you need — full material test reports and heat traceability come standard from our shop.
Materials.
Representative capabilities — every item is manufactured or certified to your specification. Confirm requirements with our estimating team.
