Dimensional data for M18 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.
M18 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 |
|---|---|---|---|---|---|---|
| M18 | 2.5 | 27.0 | 29.56 | 15.8 | Grade C | ISO 4034 / DIN 555 |
Spanner & Drive for M18 Hex Nuts, Grade C
M18 Hex Nuts, Grade C have a width across flats of 27.0 mm — fit a 27.0 mm open-ended spanner or socket. Prefer a 6-point socket over a 12-point: it loads the corners of the 27.0 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 M18
| Class 8.8 (dry, ~µ 0.125) | ≈ 297 Nm |
|---|---|
| Class 10.9 (dry, ~µ 0.125) | ≈ 423 Nm |
| Class 12.9 (dry, ~µ 0.125) | ≈ 495 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 M18
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 M18 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 M18 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 M18
Pair M18 with the matching M18 bolt or screw, plus a M18 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 M18 hex nuts, grade c. Thread size is the obvious variable and rarely the interesting one — height for clearance, across-flats for the tool already in the cell, and the locking feature for the vibration actually present. Made by cold heading or tapping.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
