Dimensional and assembly data for M5 Hex Bolt to GB/T 6173 / ISO 8675. Includes head size and width across flats, clearance-hole and tapping-drill diameters, tightening torque per property class, and the sizes to step up or down to when the joint requires it.
M5 Dimensional Row (GB/T 6173 / ISO 8675)
| Size | Pitch (mm) | Nominal diameter d (mm) | Length L (mm) | Width across flats s (mm) | Width across corners e (mm) | Head height k (mm) |
|---|---|---|---|---|---|---|
| M5 | 0.8 | 5 | 30 | 8.0 | 8.79 | 3.5 |
Spanner & Drive for M5 Hex Bolt — GB/T 6173 / ISO 8675 (Series 057)
M5 Hex Bolt — GB/T 6173 / ISO 8675 (Series 057) have a width across flats of 8.0 mm — fit a 8.0 mm open-ended spanner or socket. Prefer a 6-point socket over a 12-point: it loads the corners of the 8.0 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 M5
| Coarse-thread pitch (ISO 724) | 0.8 mm |
|---|---|
| Through-hole / clearance (ISO 273 medium) | 5.5 mm |
| Tapping drill, coarse thread | 4.2 mm |
Tightening Torque for M5
| Class 8.8 (dry, ~µ 0.125) | ≈ 5.9 Nm |
|---|---|
| Class 10.9 (dry, ~µ 0.125) | ≈ 8.7 Nm |
| Class 12.9 (dry, ~µ 0.125) | ≈ 10 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 M5
| Tensile stress area As (ISO 724) | 14.2 mm² |
|---|---|
| Proof load, class 8.8 | 8.2 kN |
| Proof load, class 10.9 | 12 kN |
| Proof load, class 12.9 | 14 kN |
| Min. ultimate tensile load, class 8.8 | 11 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.
M5 Hex Bolt — GB/T 6173 / ISO 8675 (Series 057) Weight
A steel M5 hex bolt at the listed 30 mm length weighs approximately 6.1 g each — about 6.1 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 M5 Hex Bolt — GB/T 6173 / ISO 8675 (Series 057)
- 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 M5 the joint is sensitive to over-torque — use a torque-limiting driver and check the head doesn't bury into a softer counterpart.
When to Step Up or Down from M5
When the joint preload approaches the proof load of M5 class 8.8, step up to M6 class 8.8 (or move to M5 class 10.9). When the joint is over-specified, M4 often saves weight and cost without losing the safety margin.
Custom manufacturing · Made to drawing
Need hex bolt in a size this table does not list?
This page covers M5 hex 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.
