This page covers M3 Hex Socket Cone Point Set Screw to GB/T 78 / ISO 4027: the full dimensional row, hole and tool sizes, proof-load data and typical applications. All values are taken from the governing standards (GB/T 78 / ISO 4027 together with ISO 273, ISO 724 and ISO 898-1 where applicable).
M3 Dimensional Row (GB/T 78 / ISO 4027)
| Size | Pitch (mm) | Length L (mm) | Hex socket s (mm) | Engagement depth t min (mm) | Point diameter dp (mm) | Reference standard |
|---|---|---|---|---|---|---|
| M3 | 0.5 | 6 | 1.5 | 1.4 | 2.0 | ISO 4026-4029 / GB/T 77-79 |
Spanner & Drive for M3 Hex Socket Cone Point Set Screw — GB/T 78 / ISO 4027 (Series 027)
The hex socket for M3 Hex Socket Cone Point Set Screw — GB/T 78 / ISO 4027 (Series 027) 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 Hex Socket Cone Point Set Screw — GB/T 78 / ISO 4027 (Series 027) Weight
A steel M3 hex socket cone point set screw at the listed 6 mm length weighs approximately 0.1 g each — about 0.1 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 Hex Socket Cone Point Set Screw — GB/T 78 / ISO 4027 (Series 027)
M3 Hex Socket Cone Point Set Screw — GB/T 78 / ISO 4027 (Series 027) are commonly specified for electronics, PCB hardware, optical mounts and small-scale machinery.
Installation Tips for M3 Hex Socket Cone Point Set Screw — GB/T 78 / ISO 4027 (Series 027)
- 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.
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.
