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. Use a 6-point socket for tight clearances and to reduce rounding; for repeated assembly choose a torque wrench so the joint preload is repeatable.
Common Applications for M33 Hex Bolts
M33 Hex Bolts are commonly specified for structural steelwork, heavy machinery foundations and large flange joints.
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.
- 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 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.
