M20 Hex Nut are manufactured to GB/T 6170 / ISO 4032 with a coarse thread pitch of 2.5 mm. This page lists the controlling dimensions for the M20 size — head geometry, width across flats, matching spanner size — together with the clearance hole, tapping drill and tightening torque used at assembly.
M20 Dimensional Row (GB/T 6170 / ISO 4032)
| Size | Pitch (mm) | Width across flats s (mm) | Width across corners e (mm) | Nut height m (mm) | Reference standard |
|---|---|---|---|---|---|
| M20 | 2.5 | 30.0 | 33.53 | 18.0 | ISO 4032 / GB/T 6170 |
Spanner & Drive for M20 Hex Nut — GB/T 6170 / ISO 4032 (Series 059)
M20 Hex Nut — GB/T 6170 / ISO 4032 (Series 059) have a width across flats of 30.0 mm — fit a 30.0 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 M20 Hex Nut — GB/T 6170 / ISO 4032 (Series 059)
M20 Hex Nut — GB/T 6170 / ISO 4032 (Series 059) are commonly specified for structural joints, flange connections and heavy equipment foundations.
Mating Parts for M20
Pair M20 with the matching M20 bolt or screw, plus a M20 flat washer where required to distribute load on softer materials.
When to Step Up or Down from M20
When the joint preload approaches the proof load of M20 class 8.8, step up to M24 class 8.8 (or move to M20 class 10.9). When the joint is over-specified, M16 often saves weight and cost without losing the safety margin.