When you need Heavy Hex Socket Head Cap Screw — GB/T 1228 / ASTM A325 (Series 046) in the M8 size, the controlling values come from GB/T 1228 / ASTM A325. This page lists them in one place — pitch, head geometry, tool size and the matching hole.
M8 Dimensional Row (GB/T 1228 / ASTM A325)
| Size | Pitch (mm) | Length L (mm) | Head diameter dk (mm) | Head height k (mm) | Hex socket s (mm) | Reference standard |
|---|---|---|---|---|---|---|
| M8 | 1.25 | 50 | 13.0 | 8 | 6.0 | ISO 4762 / GB/T 70.1 |
Spanner & Drive for M8 Heavy Hex Socket Head Cap Screw — GB/T 1228 / ASTM A325 (Series 046)
The hex socket for M8 Heavy Hex Socket Head Cap Screw — GB/T 1228 / ASTM A325 (Series 046) is shown in the spec table — use the matching Allen / hex key (an ISO 2936 hex key set covers the full range). A T-handle Allen key gives the best feel for setting preload by feel; for production work use a torque-controlled driver.
Hole Sizes for M8
| Coarse-thread pitch (ISO 724) | 1.25 mm |
|---|---|
| Through-hole / clearance (ISO 273 medium) | 9 mm |
| Tapping drill, coarse thread | 6.8 mm |
Tightening Torque for M8
| Class 8.8 (dry, ~µ 0.125) | ≈ 25 Nm |
|---|---|
| Class 10.9 (dry, ~µ 0.125) | ≈ 35 Nm |
| Class 12.9 (dry, ~µ 0.125) | ≈ 41 Nm |
Indicative dry-joint values. Lubrication can lower the required torque by 15–25%. Always confirm against the joint design, especially when going up a strength class.
Common Applications for M8 Heavy Hex Socket Head Cap Screw — GB/T 1228 / ASTM A325 (Series 046)
M8 Heavy Hex Socket Head Cap Screw — GB/T 1228 / ASTM A325 (Series 046) are commonly specified for machine assembly, general engineering, plant maintenance and OEM equipment.
Installation Tips for M8 Heavy Hex Socket Head Cap Screw — GB/T 1228 / ASTM A325 (Series 046)
- Use a quality Allen key fully seated in the socket — partial engagement is the most common cause of stripped sockets at this size.
- For countersunk and button-head variants, chamfer the through-hole to seat the head flush without preloading the head/shank fillet.
Mating Parts for M8
For M8, pair with a M8 hex nut (ISO 4032 / DIN 934) and, where used, a M8 flat washer (ISO 7089 / DIN 125A) under the head and under the nut.