The M18 size of Hex Nuts is dimensioned by ISO 4032 / ISO 4033. 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.
M18 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 |
|---|---|---|---|---|---|---|
| M18 | 2.5 | 27.0 | 29.56 | 15.8 | - | ISO 4032 (Style1) / ISO 4033 (Style2, M5-M36 preferred sizes) |
Spanner & Drive for M18 Hex Nuts
M18 Hex Nuts have a width across flats of 27.0 mm — fit a 27.0 mm open-ended spanner or socket. A 6-point socket grips all six flats of the 27.0 mm hex and is what to reach for once a fastener has been on and off a few times; a 12-point ring spanner starts rounding a worn head. For repeatable preload, torque rather than feel.
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
- 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 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 in a size this table does not list?
This page covers M18 hex nuts. Height and across-flats are the two most often changed — a thinner nut for clearance, a larger hex for a tool that is already on the line. Made by cold heading or tapping.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
