The M8 size of Hex Nuts, Grade C is dimensioned by ISO 4034. The table below gives the dimensional row from the standard, followed by 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.
M8 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 |
|---|---|---|---|---|---|---|
| M8 | 1.25 | 13.0 | 14.2 | 6.8 | Grade C | ISO 4034 / DIN 555 |
Spanner & Drive for M8 Hex Nuts, Grade C
M8 Hex Nuts, Grade C have a width across flats of 13.0 mm — fit a 13.0 mm open-ended spanner or socket. Prefer a 6-point socket over a 12-point: it loads the corners of the 13.0 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 M8
| Class 8.8 (dry, ~µ 0.125) | ≈ 24 Nm |
|---|---|
| Class 10.9 (dry, ~µ 0.125) | ≈ 36 Nm |
| Class 12.9 (dry, ~µ 0.125) | ≈ 42 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 M8
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 M8 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.
When to Step Up or Down from M8
When the joint preload approaches the proof load of M8 class 8.8, step up to M10 class 8.8 (or move to M8 class 10.9). When the joint is over-specified, M6 often saves weight and cost without losing the safety margin.
Custom manufacturing · Made to drawing
Need hex nuts, grade c in a size this table does not list?
This page covers M8 hex nuts, grade c. 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.
