Dimensional data for M20 Hex Nuts to ISO 4032 / ISO 4033, with the drive and the installation notes for this type.
Values are taken from the governing standard rather than from a general machine-thread table, because this type is not selected on one.
M20 Dimensional Row (ISO 4032 / ISO 4033)
| Size | Pitch (mm) | Width across flats s (mm) | Width across corners e min (mm) | Nut height m style 1 (mm) | Nut height m style 2 (mm) | Reference standard |
|---|---|---|---|---|---|---|
| M20 | 2.5 | 30.0 | 32.95 | 18.0 | 20.3 | ISO 4032 (Style1) / ISO 4033 (Style2, M5-M36 preferred sizes) |
Spanner & Drive for M20 Hex Nuts
M20 Hex Nuts have a width across flats of 30.0 mm — fit a 30.0 mm open-ended spanner or socket. Prefer a 6-point socket over a 12-point: it loads the corners of the 30.0 mm hex far less, which matters on plated heads and on anything that will be re-used. Set preload with a torque wrench rather than by arm.
Tightening Torque for M20
| Class 8.8 (dry, ~µ 0.125) | ≈ 420 Nm |
|---|---|
| Class 10.9 (dry, ~µ 0.125) | ≈ 598 Nm |
| Class 12.9 (dry, ~µ 0.125) | ≈ 700 Nm |
Indicative dry-joint values. Lubrication can lower the required torque by 15–25%. Always confirm against the joint design, especially when going up a strength class.
Proof Load & Strength for M20
Nuts are graded to ISO 898-2 by the proof load the nut itself will hold (classes 04, 05, 5, 6, 8, 10 and 12), not by the 8.8 / 10.9 / 12.9 scale used for bolts. A class-8 nut is the correct mate for a class-8.8 bolt, and the joint is designed on the bolt, so no bolt-tension figure is quoted here.
Installation Tips for M20 Hex Nuts
- Use a 6-point socket where access allows — 12-point sockets are more prone to rounding the corners on smaller sizes.
- A flanged head is its own washer. Adding a flat one under it lifts the serrations clear of the surface they are meant to bite, which is the whole locking mechanism gone.
- 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.
Custom manufacturing · Made to drawing
Need hex nuts in a size this table does not list?
This page covers M20 hex nuts. Locking method is specifiable independently of the rest: nylon insert, all-metal deformed thread, serrated flange, or none. Made by cold heading or tapping.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
