Selecting Hex Nut — GB/T 6170 / ISO 4032 (Series 059), M20, in GB/T 6170 / ISO 4032: the dimensional row from the standard plus the tools and hole sizes follow. Use them with the technical drawing below — the drawing redraws to the exact size you pick.
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.
Installation Tips for M20 Hex Nut — GB/T 6170 / ISO 4032 (Series 059)
- Use a 6-point socket where access allows — 12-point sockets are more prone to rounding the corners on smaller sizes.
- On flanged or serrated variants, do NOT add a separate flat washer — the flange already spreads the load and the washer can defeat the locking serrations.
- At M20 the stretch in the bolt becomes the controlling factor — for critical joints, use angle-controlled or stretch-controlled tightening instead of pure torque.
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.