Head diameter, head height, hex key size and key depth for inch socket head cap screws, #0 to 2″. ASME B18.3.
The numbers behind a socket head cap screw (“Allen head”). J is the hex key (Allen wrench) that fits it; A is the room the round head needs, the counterbore it sits in; H is the head height — on a socket head it equals the screw’s own diameter; T is how deep the key goes in. Inches throughout.
Letters match the table. J hex key size, A head diameter, H head height, T key engagement depth (minimum).
| Size | Hex key J | Head dia. A max | A min | Head height H max | H min | Key depth T min |
|---|---|---|---|---|---|---|
| #0 | .050″ | 0.096 | 0.091 | 0.060 | 0.057 | 0.025 |
| #1 | 1/16″ | 0.118 | 0.112 | 0.073 | 0.070 | 0.031 |
| #2 | 5/64″ | 0.140 | 0.134 | 0.086 | 0.083 | 0.038 |
| #3 | 5/64″ | 0.161 | 0.154 | 0.099 | 0.095 | 0.044 |
| #4 | 3/32″ | 0.183 | 0.176 | 0.112 | 0.108 | 0.051 |
| #5 | 3/32″ | 0.205 | 0.198 | 0.125 | 0.121 | 0.057 |
| #6 | 7/64″ | 0.226 | 0.218 | 0.138 | 0.134 | 0.064 |
| #8 | 9/64″ | 0.270 | 0.262 | 0.164 | 0.159 | 0.077 |
| #10 | 5/32″ | 0.312 | 0.303 | 0.190 | 0.185 | 0.090 |
| 1/4″ | 3/16″ | 0.375 | 0.365 | 0.250 | 0.244 | 0.120 |
| 5/16″ | 1/4″ | 0.469 | 0.457 | 0.312 | 0.306 | 0.151 |
| 3/8″ | 5/16″ | 0.562 | 0.550 | 0.375 | 0.368 | 0.182 |
| 7/16″ | 3/8″ | 0.656 | 0.642 | 0.438 | 0.430 | 0.213 |
| 1/2″ | 3/8″ | 0.750 | 0.735 | 0.500 | 0.492 | 0.245 |
| 5/8″ | 1/2″ | 0.938 | 0.921 | 0.625 | 0.616 | 0.307 |
| 3/4″ | 5/8″ | 1.125 | 1.107 | 0.750 | 0.740 | 0.370 |
| 7/8″ | 3/4″ | 1.312 | 1.293 | 0.875 | 0.864 | 0.432 |
| 1″ | 3/4″ | 1.500 | 1.479 | 1.000 | 0.988 | 0.495 |
| 1-1/8″ | 7/8″ | 1.688 | 1.665 | 1.125 | 1.111 | 0.557 |
| 1-1/4″ | 7/8″ | 1.875 | 1.852 | 1.250 | 1.236 | 0.620 |
| 1-3/8″ | 1″ | 2.062 | 2.038 | 1.375 | 1.360 | 0.682 |
| 1-1/2″ | 1″ | 2.250 | 2.224 | 1.500 | 1.485 | 0.745 |
| 1-3/4″ | 1-1/4″ | 2.625 | 2.597 | 1.750 | 1.734 | 0.870 |
| 2″ | 1-1/2″ | 3.000 | 2.970 | 2.000 | 1.983 | 0.995 |
Thread sizes and pitches are on the thread pitch chart.
Strength: this chart is size only. Alloy-steel socket head cap screws are made to ASTM A574 → — proof and tensile strength, and the minimum loads for each size, are on that page. Stainless socket heads are not A574.
Quick answers
- What size Allen wrench fits a 1/4" socket head cap screw?
- A 3/16″ hex key (Allen wrench).
- What hex key goes with each socket head cap screw size?
- #0 – .050″, #1 – 1/16″, #2 – 5/64″, #3 – 5/64″, #4 – 3/32″, #5 – 3/32″, #6 – 7/64″, #8 – 9/64″, #10 – 5/32″, 1/4″ – 3/16″, 5/16″ – 1/4″, 3/8″ – 5/16″, 7/16″ – 3/8″, 1/2″ – 3/8″, 5/8″ – 1/2″, 3/4″ – 5/8″, 7/8″ – 3/4″, 1″ – 3/4″, 1-1/8″ – 7/8″, 1-1/4″ – 7/8″, 1-3/8″ – 1″, 1-1/2″ – 1″, 1-3/4″ – 1-1/4″, 2″ – 1-1/2″.
- How tall is the head on a socket head cap screw?
- The head height equals the screw’s diameter — a 3/8″ socket head cap screw has a head 0.375″ tall and 0.562″ across.
- How deep does the hex key go into a socket head cap screw?
- At least 0.120″ on a 1/4″, 0.245″ on a 1/2″ and 0.495″ on a 1″ (key engagement T, minimum).