Dimensional and assembly data for M20 Hex Slotted Nut to GB/T 6181 / ISO 4035. 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.
M20 Dimensional Row (GB/T 6181 / ISO 4035)
| 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 | 10.0 | ISO 4035 / GB/T 6172 |
Spanner & Drive for M20 Hex Slotted Nut — GB/T 6181 / ISO 4035 (Series 054)
M20 Hex Slotted Nut — GB/T 6181 / ISO 4035 (Series 054) 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 Slotted Nut — GB/T 6181 / ISO 4035 (Series 054)
M20 Hex Slotted Nut — GB/T 6181 / ISO 4035 (Series 054) are commonly specified for structural joints, flange connections and heavy equipment foundations.
Installation Tips for M20 Hex Slotted Nut — GB/T 6181 / ISO 4035 (Series 054)
- 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.
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.