Dimensional and assembly data for M3 Torx Countersunk Head Screw to GB/T 2673 / ISO 14583. Includes head size and width across flats, clearance-hole and tapping-drill diameters, tightening torque per property class, and the sizes to step up or down to when the joint requires it.
M3 Dimensional Row (GB/T 2673 / ISO 14583)
| Size | Pitch (mm) | Length L (mm) | Head diameter dk (mm) | Head height k (mm) | Cross recess | Countersink angle (deg) | Reference standard |
|---|---|---|---|---|---|---|---|
| M3 | 0.5 | 20 | 5.6 | 1.65 | PH1 | 90 | ISO 7046 / GB/T 819 |
Spanner & Drive for M3 Torx Countersunk Head Screw — GB/T 2673 / ISO 14583 (Series 023)
The hex socket for M3 Torx Countersunk Head Screw — GB/T 2673 / ISO 14583 (Series 023) 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.
Proof Load & Strength for M3
| Tensile stress area As (ISO 898-1) | 5.03 mm² |
|---|---|
| Proof load, class 8.8 | 2.9 kN |
| Proof load, class 10.9 | 4.2 kN |
| Proof load, class 12.9 | 4.9 kN |
| Min. ultimate tensile, class 8.8 | 4 kN |
Proof load = stress area × proof stress per ISO 898-1. Design joints so the working preload stays below the proof load of the selected class.
M3 Torx Countersunk Head Screw — GB/T 2673 / ISO 14583 (Series 023) Weight
A steel M3 torx countersunk head screw at the listed 20 mm length weighs approximately 3.9 g each — about 3.9 kg per 1,000 pieces. Stainless A2/A4 weighs roughly the same (density 7.9–8.0 g/cm³). Actual weight varies slightly with head form, thread and finish; use this figure for freight estimation only.
Common Applications for M3 Torx Countersunk Head Screw — GB/T 2673 / ISO 14583 (Series 023)
M3 Torx Countersunk Head Screw — GB/T 2673 / ISO 14583 (Series 023) are commonly specified for electronics, PCB hardware, optical mounts and small-scale machinery.
Installation Tips for M3 Torx Countersunk Head Screw — GB/T 2673 / ISO 14583 (Series 023)
- 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 M3 the joint is sensitive to over-torque — use a torque-limiting driver and check the head doesn't bury into a softer counterpart.
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.