This page covers M33 Hex Bolts to ISO 4014 / ISO 4017: the full dimensional row, hole and tool sizes, proof-load data and typical applications. All values are taken from the governing standards (ISO 4014 / ISO 4017 together with ISO 273, ISO 724 and ISO 898-1 where applicable).
M33 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 |
|---|---|---|---|---|---|---|---|
| M33 | 3.5 | 50.0 | 55.37 | 21.0 | 33.0 | ISO 4014/4017 | Partial / fully threaded |
Spanner & Drive for M33 Hex Bolts
M33 Hex Bolts have a width across flats of 50.0 mm — fit a 50.0 mm open-ended spanner or socket. Prefer a 6-point socket over a 12-point: it loads the corners of the 50.0 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 M33
| Coarse-thread pitch (ISO 724) | 3.5 mm |
|---|---|
| Through-hole / clearance (ISO 273 medium) | 36 mm |
| Tapping drill, coarse thread | 29.5 mm |
Tightening Torque for M33
| Class 8.8 (dry, ~µ 0.125) | ≈ 1964 Nm |
|---|---|
| Class 10.9 (dry, ~µ 0.125) | ≈ 2797 Nm |
| Class 12.9 (dry, ~µ 0.125) | ≈ 3273 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 M33
| Tensile stress area As (ISO 724) | 694 mm² |
|---|---|
| Proof load, class 8.8 | 416 kN |
| Proof load, class 10.9 | 576 kN |
| Proof load, class 12.9 | 673 kN |
| Min. ultimate tensile load, class 8.8 | 576 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 M33 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 M33 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 M33
For M33, pair with a M33 hex nut (ISO 4032 / DIN 934) and, where used, a M33 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 M33 hex bolts. Where the standard stops, the drawing takes over: fine pitches, left-hand threads, partial threading, and property classes above the catalogued grade where material and heat treatment allow. Made by cold heading or hot forging.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
