Dimensional data for M20 Hex Nuts, Grade C to ISO 4034, 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 4034)
| Size | Pitch (mm) | Width across flats s (mm) | Width across corners e min (mm) | Nut height m (mm) | Product grade | Reference standard |
|---|---|---|---|---|---|---|
| M20 | 2.5 | 30.0 | 33.53 | 18.0 | Grade C | ISO 4034 / DIN 555 |
Spanner & Drive for M20 Hex Nuts, Grade C
M20 Hex Nuts, Grade C 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, Grade C
- 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, grade c in a size this table does not list?
This page covers M20 hex nuts, grade c. Thread, height, across-flats, property class, locking feature and flange form can all be varied, including thread sizes the standard series does not run to. Made by cold heading or tapping.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
