Socket Head Cap Screw (SHCS) Dimensions
Socket head cap screws are the go-to fastener for machine design. Their cylindrical head fits into a counterbore, allowing the screw to sit flush with or below the surface — critical when you need clearance for moving parts or a clean look.
All dimensions per ASME B18.3:
| Screw Size | Head Ø (in) | Head Height (in) | Hex Key Size (in) | Counterbore Ø (in) | Counterbore Depth (in) |
|---|---|---|---|---|---|
| #0 | 0.096 | 0.060 | 0.050 | 0.125 | 0.068 |
| #1 | 0.118 | 0.073 | 1/16 | 0.156 | 0.084 |
| #2 | 0.140 | 0.086 | 5/64 | 0.172 | 0.100 |
| #3 | 0.161 | 0.099 | 5/64 | 0.203 | 0.112 |
| #4 | 0.183 | 0.112 | 3/32 | 0.219 | 0.128 |
| #5 | 0.205 | 0.125 | 3/32 | 0.250 | 0.140 |
| #6 | 0.226 | 0.138 | 7/64 | 0.281 | 0.156 |
| #8 | 0.270 | 0.164 | 9/64 | 0.328 | 0.188 |
| #10 | 0.312 | 0.190 | 5/32 | 0.375 | 0.218 |
| 1/4″ | 0.375 | 0.250 | 3/16 | 0.438 | 0.278 |
| 5/16″ | 0.469 | 0.312 | 1/4 | 0.547 | 0.347 |
| 3/8″ | 0.562 | 0.375 | 5/16 | 0.656 | 0.415 |
| 7/16″ | 0.656 | 0.438 | 3/8 | 0.766 | 0.484 |
| 1/2″ | 0.750 | 0.500 | 3/8 | 0.875 | 0.552 |
| 5/8″ | 0.938 | 0.625 | 1/2 | 1.094 | 0.689 |
| 3/4″ | 1.125 | 0.750 | 5/8 | 1.312 | 0.828 |
| 7/8″ | 1.312 | 0.875 | 3/4 | 1.531 | 0.963 |
| 1″ | 1.500 | 1.000 | 3/4 | 1.750 | 1.100 |
Counterbore Design Rules
- Counterbore diameter = Head diameter + 1/16″ (minimum radial clearance)
- Counterbore depth = Head height + 0.010″–0.030″ (slight recess below surface)
- Through-hole = Use close-fit clearance from tap drill charts
SHCS vs. Hex Cap Bolts
| Feature | Socket Head Cap Screw | Hex Cap Bolt |
|---|---|---|
| Head profile | Cylindrical, flush-mount | Hex, protrudes above surface |
| Typical grade | Alloy steel, 180 ksi min tensile | Grade 5 (120 ksi) or Grade 8 (150 ksi) |
| Drive tool | Hex key (Allen wrench) | Wrench or socket |
| Cost | Higher | Lower |
| Best for | Machine design, tight spaces, precision | Structural, general assembly |
Material & Strength
Standard SHCS are alloy steel per ASTM A574 — minimum 180,000 psi tensile strength. That’s stronger than Grade 8 bolts. They’re also available in:
- 18-8 Stainless — corrosion resistance, ~70 ksi tensile (much weaker than alloy)
- Titanium — lightweight, corrosion resistant, expensive
- Nylon — electrical isolation, chemical resistance
Related: Hex Cap Bolt Dimensions | Bolt Grade Identification | UNC Tap Drill Sizes