M3 Hex Nut, Fine Pitch (GB/T 6171 / ISO 8673) are specified by thread size, length and head dimensions. The M3 row from the standard is reproduced below, followed by the drill sizes, spanner size and torque values used when installing this size.
M3 Dimensional Row (GB/T 6171 / ISO 8673)
| Size | Pitch (mm) | Width across flats s (mm) | Width across corners e (mm) | Nut height m (mm) | Reference standard |
|---|---|---|---|---|---|
| M3 | 0.5 | 5.5 | 6.01 | 2.4 | ISO 4032 / GB/T 6170 |
Spanner & Drive for M3 Hex Nut, Fine Pitch — GB/T 6171 / ISO 8673 (Series 067)
M3 Hex Nut, Fine Pitch — GB/T 6171 / ISO 8673 (Series 067) have a width across flats of 5.5 mm — fit a 5.5 mm open-ended spanner or socket. Use a 6-point socket for tight clearances and to reduce rounding; for repeated assembly choose a torque wrench so the joint preload is repeatable.
Common Applications for M3 Hex Nut, Fine Pitch — GB/T 6171 / ISO 8673 (Series 067)
M3 Hex Nut, Fine Pitch — GB/T 6171 / ISO 8673 (Series 067) are commonly specified for paired with the same-size screws on PCB hardware, light enclosures and small-scale assemblies.
Mating Parts for M3
Pair M3 with the matching M3 bolt or screw, plus a M3 flat washer where required to distribute load on softer materials.
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.