Dimensional and assembly data for M3 Hex Bolts to ISO 4014 / ISO 4017. 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.
M3 Dimensional Row (ISO 4014 / ISO 4017)
| Size | Pitch coarse (mm) | Width across flats s (mm) | Width across corners e min (mm) | Head height k nom (mm) | Nominal diameter d (mm) | Reference standard | Notes |
|---|---|---|---|---|---|---|---|
| M3 | 0.5 | 5.5 | 6.01 | 2.0 | 3.0 | ISO 4014/4017 | Fully threaded |
Spanner & Drive for M3 Hex Bolts
M3 Hex Bolts have a width across flats of 5.5 mm — fit a 5.5 mm open-ended spanner or socket. In tight access a 6-point socket on the 5.5 mm flats gives the most engagement per degree of swing. Where the joint is torqued to a figure, a click wrench is the only way to reproduce it across a batch.
Hole Sizes for M3
| Coarse-thread pitch (ISO 724) | 0.5 mm |
|---|---|
| Through-hole / clearance (ISO 273 medium) | 3.4 mm |
| Tapping drill, coarse thread | 2.5 mm |
Tightening Torque for M3
| Class 8.8 (dry, ~µ 0.125) | ≈ 1.3 Nm |
|---|---|
| Class 10.9 (dry, ~µ 0.125) | ≈ Nm |
| Class 12.9 (dry, ~µ 0.125) | ≈ 2.2 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 M3
| Tensile stress area As (ISO 724) | 5 mm² |
|---|---|
| Proof load, class 8.8 | 2.9 kN |
| Proof load, class 12.9 | 4.9 kN |
| Min. ultimate tensile load, class 8.8 | 4 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.
Installation Tips for M3 Hex Bolts
- Use a 6-point socket where access allows — 12-point sockets are more prone to rounding the corners on smaller sizes.
- Serrated flanges need to sit directly on the joint face. A washer between the two removes the bite and leaves an ordinary bolted joint that is believed to be a locking one.
- At M3 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 M3
When the joint preload approaches the proof load of M3 class 8.8, step up to M4 class 8.8 (or move to M3 class 10.9). When the joint is over-specified, M2 often saves weight and cost without losing the safety margin.
Custom manufacturing · Made to drawing
Need hex bolts in a size this table does not list?
This page covers M3 hex bolts. Thread size and pitch, length, property class, drive form, head geometry and head marking are all specifiable — the standard part is where it starts, not where it stops. Made by cold heading or hot forging.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
