M56 Hex Bolts (ISO 4014 / ISO 4017) are specified by thread size, length and head dimensions. The M56 row from the standard is reproduced below, followed by the drill sizes, spanner size and torque values used when installing this size.
M56 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 |
|---|---|---|---|---|---|---|---|
| M56 | 5.5 | 85.0 | 93.56 | 35.0 | 56.0 | ISO 4014 | Partial / fully threaded |
Spanner & Drive for M56 Hex Bolts
M56 Hex Bolts have a width across flats of 85.0 mm — fit a 85.0 mm open-ended spanner or socket. Prefer a 6-point socket over a 12-point: it loads the corners of the 85.0 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 M56
| Coarse-thread pitch (ISO 724) | 5.5 mm |
|---|---|
| Through-hole / clearance (ISO 273 medium) | 62 mm |
| Tapping drill, coarse thread | 50.5 mm |
Tightening Torque for M56
| 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 M56
| Tensile stress area As (ISO 724) | 2030 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 M56 Hex Bolts
- 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 M56 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 M56
For M56, pair with a M56 hex nut (ISO 4032 / DIN 934) and, where used, a M56 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 M56 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.
