When you need Socket Head Cap Screw — GB/T 5281 / ISO 7379 (Series 016) in the M3 size, the controlling values come from GB/T 5281 / ISO 7379. This page lists them in one place — pitch, head geometry, tool size and the matching hole.
M3 Dimensional Row (GB/T 5281 / ISO 7379)
| Size | Pitch (mm) | Length L (mm) | Head diameter dk (mm) | Head height k (mm) | Hex socket s (mm) | Reference standard |
|---|---|---|---|---|---|---|
| M3 | 0.5 | 20 | 5.5 | 3 | 2.5 | ISO 4762 / GB/T 70.1 |
Spanner & Drive for M3 Socket Head Cap Screw — GB/T 5281 / ISO 7379 (Series 016)
The hex socket for M3 Socket Head Cap Screw — GB/T 5281 / ISO 7379 (Series 016) 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 M3
| Coarse-thread pitch (ISO 724) | 0.5 mm |
|---|---|
| Through-hole / clearance (ISO 273 medium) | 3.4 mm |
| Tapping drill, coarse thread | 2.5 mm |
Tightening Torque for M3
| Class 8.8 (dry, ~µ 0.125) | ≈ 1.3 Nm |
|---|---|
| Class 10.9 (dry, ~µ 0.125) | ≈ 1.8 Nm |
| Class 12.9 (dry, ~µ 0.125) | ≈ 2.1 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 M3 Socket Head Cap Screw — GB/T 5281 / ISO 7379 (Series 016)
M3 Socket Head Cap Screw — GB/T 5281 / ISO 7379 (Series 016) are commonly specified for electronics, PCB hardware, optical mounts and small-scale machinery.
Mating Parts for M3
For M3, pair with a M3 hex nut (ISO 4032 / DIN 934) and, where used, a M3 flat washer (ISO 7089 / DIN 125A) under the head and under the nut.
When to Step Up or Down from M3
When the joint preload approaches the proof load of M3 class 8.8, step up to M4 class 8.8 (or move to M3 class 10.9). When the joint is over-specified, M2 often saves weight and cost without losing the safety margin.