M18 Hex Head Bolt are manufactured to GB/T 5782 / ISO 4014 with a coarse thread pitch of 2.5 mm. This page lists the controlling dimensions for the M18 size — head geometry, width across flats, matching spanner size — together with the clearance hole, tapping drill and tightening torque used at assembly.
M18 Dimensional Row (GB/T 5782 / ISO 4014)
| Size | Pitch (mm) | Nominal diameter d (mm) | Length L (mm) | Width across flats s (mm) | Width across corners e (mm) | Head height k (mm) |
|---|---|---|---|---|---|---|
| M18 | 2.5 | 18 | 100 | 27.0 | 30.14 | 11.5 |
Spanner & Drive for M18 Hex Head Bolt — GB/T 5782 / ISO 4014 (Series 002)
M18 Hex Head Bolt — GB/T 5782 / ISO 4014 (Series 002) 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.
Hole Sizes for M18
| Coarse-thread pitch (ISO 724) | 2.5 mm |
|---|---|
| Through-hole / clearance (ISO 273 medium) | 20 mm |
| Tapping drill, coarse thread | 15.5 mm |
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
| Tensile stress area As (ISO 724) | 192 mm² |
|---|---|
| Proof load, class 8.8 | 115 kN |
| Proof load, class 10.9 | 160 kN |
| Proof load, class 12.9 | 187 kN |
| Min. ultimate tensile load, class 8.8 | 160 kN |
Proof load = tensile stress area × the proof stress Sp of the class, per ISO 898-1 — Sp is a lower figure than the yield stress Rp0.2 and the two are not interchangeable. The stress area is computed from this size's own diameter and pitch, so a fine-pitch designation gives the fine-pitch figure. Design the joint so the working preload stays below the proof load of the class selected.
M18 Hex Head Bolt — GB/T 5782 / ISO 4014 (Series 002) Weight
A steel M18 hex head bolt at the listed 100 mm length weighs approximately 257 g each — about 257 kg per 1,000 pieces. Stainless A2/A4 weighs roughly the same (density 7.9–8.0 g/cm³).
Actual weight varies slightly with head form, thread and finish; use this figure for freight estimation only.
Installation Tips for M18 Hex Head Bolt — GB/T 5782 / ISO 4014 (Series 002)
- 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
For M18, pair with a M18 hex nut (ISO 4032 / DIN 934) and, where used, a M18 flat washer (ISO 7089 / DIN 125A) under the head and under the nut.
Custom manufacturing · Made to drawing
Need hex head bolt in a size this table does not list?
This page covers M18 hex head bolt. Material and finish are usually what drives a special — a grade the standard part is not stocked in, or a coating chosen against a salt-spray figure instead of a default. Made by cold heading or hot forging.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
