The M39 size of Hex Bolts is dimensioned by ISO 4014 / ISO 4017. The tables below give the dimensional row from the standard, the drill and spanner sizes that go with it, and the assembly torque per property class. The technical drawing on this page redraws to the exact values selected.
M39 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 |
|---|---|---|---|---|---|---|---|
| M39 | 4.0 | 60.0 | 66.44 | 25.0 | 39.0 | ISO 4014/4017 | Partial / fully threaded |
Spanner & Drive for M39 Hex Bolts
M39 Hex Bolts have a width across flats of 60.0 mm — fit a 60.0 mm open-ended spanner or socket. In tight access a 6-point socket on the 60.0 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 M39
| Coarse-thread pitch (ISO 724) | 4 mm |
|---|---|
| Through-hole / clearance (ISO 273 medium) | 42 mm |
| Tapping drill, coarse thread | 35 mm |
Tightening Torque for M39
| Class 8.8 (dry, ~µ 0.125) | ≈ 3265 Nm |
|---|---|
| Class 10.9 (dry, ~µ 0.125) | ≈ 4650 Nm |
| Class 12.9 (dry, ~µ 0.125) | ≈ 5442 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 M39
| Tensile stress area As (ISO 724) | 976 mm² |
|---|---|
| Proof load, class 8.8 | 585 kN |
| Proof load, class 10.9 | 810 kN |
| Proof load, class 12.9 | 946 kN |
| Min. ultimate tensile load, class 8.8 | 810 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 M39 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 M39 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 M39
For M39, pair with a M39 hex nut (ISO 4032 / DIN 934) and, where used, a M39 flat washer (ISO 7089 / DIN 125A) under the head and under the nut.
Custom manufacturing · Made to drawing
Need hex bolts in a size this table does not list?
This page covers M39 hex bolts. 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.
