M42 is one of the standard coarse-thread sizes for hex bolts, grade c under ISO 4016. The sections below reproduce the dimensional row, list the matching tools and hole sizes, and summarize where this size is normally specified.
M42 Dimensional Row (ISO 4016)
| Size | Pitch (mm) | Width across flats s (mm) | Width across corners e min (mm) | Head height k (mm) | Product grade | Reference standard |
|---|---|---|---|---|---|---|
| M42 | 4.5 | 65.0 | 71.3 | 27.05 | Grade C | ISO 4016 / DIN 601 |
Spanner & Drive for M42 Hex Bolts, Grade C
M42 Hex Bolts, Grade C have a width across flats of 65.0 mm — fit a 65.0 mm open-ended spanner or socket. A 6-point socket grips all six flats of the 65.0 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.
Hole Sizes for M42
| Coarse-thread pitch (ISO 724) | 4.5 mm |
|---|---|
| Through-hole / clearance (ISO 273 medium) | 45 mm |
| Tapping drill, coarse thread | 37.5 mm |
Tightening Torque for M42
| Class 8.8 (dry, ~µ 0.125) | ≈ Nm |
|---|---|
| Class 10.9 (dry, ~µ 0.125) | ≈ Nm |
| Class 12.9 (dry, ~µ 0.125) | ≈ 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 M42
| Tensile stress area As (ISO 724) | 1121 mm² |
|---|
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 M42 Hex Bolts, Grade C
- 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 M42 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 M42
For M42, pair with a M42 hex nut (ISO 4032 / DIN 934) and, where used, a M42 flat washer (ISO 7089 / DIN 125A) under the head and under the nut.
Custom manufacturing · Made to drawing
Need hex bolts, grade c in a size this table does not list?
This page covers M42 hex bolts, grade c. Lengths and thread lengths outside the standard table are the commonest request, followed by a drive the standard does not offer and a head marked with your own part number. Made by cold heading or hot forging.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
