M4 Heavy Hex Socket Head Cap Screw — GB/T 1228 / ASTM A325 (Series 046) is the m4-thread variant of Heavy Hex Socket Head Cap Screw — GB/T 1228 / ASTM A325 (Series 046) manufactured to GB/T 1228 / ASTM A325. This page focuses on the data engineers reach for at the bench: dimensional values for the M4 size, the spanner/drive that fits, and the assembly data you need to install it.
M4 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 |
|---|---|---|---|---|---|---|
| M4 | 0.7 | 25 | 7.0 | 4 | 3.0 | ISO 4762 / GB/T 70.1 |
Spanner & Drive for M4 Heavy Hex Socket Head Cap Screw — GB/T 1228 / ASTM A325 (Series 046)
The hex socket for M4 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 M4
| Coarse-thread pitch (ISO 724) | 0.7 mm |
|---|---|
| Through-hole / clearance (ISO 273 medium) | 4.5 mm |
| Tapping drill, coarse thread | 3.3 mm |
Tightening Torque for M4
| Class 8.8 (dry, ~µ 0.125) | ≈ 2.9 Nm |
|---|---|
| Class 10.9 (dry, ~µ 0.125) | ≈ 4.1 Nm |
| Class 12.9 (dry, ~µ 0.125) | ≈ 4.9 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.
Installation Tips for M4 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.
- At M4 the joint is sensitive to over-torque — use a torque-limiting driver and check the head doesn't bury into a softer counterpart.
Mating Parts for M4
For M4, pair with a M4 hex nut (ISO 4032 / DIN 934) and, where used, a M4 flat washer (ISO 7089 / DIN 125A) under the head and under the nut.
When to Step Up or Down from M4
When the joint preload approaches the proof load of M4 class 8.8, step up to M5 class 8.8 (or move to M4 class 10.9). When the joint is over-specified, M3 often saves weight and cost without losing the safety margin.