M20 is one of the standard coarse-thread sizes for thin hex nut under GB/T 6170 / ISO 4032. The sections below reproduce the dimensional row, list the matching tools and hole sizes, and summarize where this size is normally specified.
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 | 10.0 | ISO 4035 / GB/T 6172 |
Spanner & Drive for M20 Thin Hex Nut — GB/T 6170 / ISO 4032 (Series 058)
M20 Thin Hex Nut — GB/T 6170 / ISO 4032 (Series 058) 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 Thin Hex Nut — GB/T 6170 / ISO 4032 (Series 058)
M20 Thin Hex Nut — GB/T 6170 / ISO 4032 (Series 058) are commonly specified for structural joints, flange connections and heavy equipment foundations.
Installation Tips for M20 Thin Hex Nut — GB/T 6170 / ISO 4032 (Series 058)
- 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.