M24 is one of the standard coarse-thread sizes for hex flange bolts under ISO 1665 / DIN 6921. The sections below reproduce the dimensional row, list the matching tools and hole sizes, and summarize where this size is normally specified.
M24 Dimensional Row (ISO 1665 / DIN 6921)
| Size | Pitch (mm) | Flange diameter dc (mm) | Head height k (mm) | Width across flats s (mm) | Reference standard |
|---|---|---|---|---|---|
| M24 | 3.0 | 51.1 | 21.0 | 36.0 | ISO 1665 / DIN 6921 |
Spanner & Drive for M24 Hex Flange Bolts
M24 Hex Flange Bolts have a width across flats of 36.0 mm — fit a 36.0 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.
Hole Sizes for M24
| Coarse-thread pitch (ISO 724) | 3 mm |
|---|---|
| Through-hole / clearance (ISO 273 medium) | 26 mm |
| Tapping drill, coarse thread | 21 mm |
Tightening Torque for M24
| Class 8.8 (dry, ~µ 0.125) | ≈ 710 Nm |
|---|---|
| Class 10.9 (dry, ~µ 0.125) | ≈ 1000 Nm |
| Class 12.9 (dry, ~µ 0.125) | ≈ 1200 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 M24
| Tensile stress area As (ISO 898-1) | 353 mm² |
|---|---|
| Proof load, class 8.8 | 212 kN |
| Proof load, class 10.9 | 293 kN |
| Proof load, class 12.9 | 342 kN |
| Min. ultimate tensile, class 8.8 | 282 kN |
Proof load = stress area × proof stress per ISO 898-1. Design joints so the working preload stays below the proof load of the selected class.
Common Applications for M24 Hex Flange Bolts
M24 Hex Flange Bolts are commonly specified for structural steelwork, heavy machinery foundations and large flange joints.
Installation Tips for M24 Hex Flange 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 M24 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 M24
For M24, pair with a M24 hex nut (ISO 4032 / DIN 934) and, where used, a M24 flat washer (ISO 7089 / DIN 125A) under the head and under the nut.