M24 Bolt Specifications
Verified by Rachel Mayfield, Supply Chain Analyst - April 2026
Every dimension, torque value, and thread specification for the M24 metric bolt in one reference card. M24 Bolt Specifications M24 is one of the most common metric fastener sizes in UK engineering, used across heavy structural and high-load joints.
| Property | Value | Standard |
|---|---|---|
| Nominal diameter | 24.0 mm | ISO 261 |
| Coarse pitch | 3.0 mm | ISO 261 |
| Fine pitch | 2.0 mm | ISO 261 |
| Tap drill (coarse, 75% engagement) | 21.0 mm | ISO 2306 |
| Tap drill (fine) | 22.0 mm | ISO 2306 |
| Clearance hole - close | 25.0 mm | ISO 273 |
| Clearance hole - medium | 26.0 mm | ISO 273 |
| Clearance hole - coarse | 28.0 mm | ISO 273 |
| Hex head A/F (spanner size) | 36.0 mm | ISO 4014 |
| Hex head height | 15.0 mm | ISO 4014 |
| Socket head cap screw head dia | 36.0 mm | ISO 4762 |
| Socket head hex key size | 19.0 mm | ISO 4762 |
| Tensile stress area | 353 mm^2 | ISO 898-1 |
| Minimum tensile strength 8.8 | 800 MPa | ISO 898-1 |
| Minimum tensile strength 10.9 | 1040 MPa | ISO 898-1 |
| Proof load 8.8 | 204.7 kN | ISO 898-1 |
| Proof load 10.9 | 293.0 kN | ISO 898-1 |
| Torque dry, class 8.8 | 690 Nm | VDI 2230 |
| Torque dry, class 10.9 | 970 Nm | VDI 2230 |
| Torque dry, class 12.9 | 1140 Nm | VDI 2230 |
M24 thread pitch
Standard M24 bolts use a 3.0 mm coarse pitch. Fine pitch M24 x 2.0 is used where vibration resistance matters or in thin-wall components. Coarse pitch is the default - if a drawing says M24 with no pitch specified, it means M24 x 3.0 coarse.
M24 tap drill size
For M24 x 3.0 coarse pitch with 75% thread engagement, drill 21.0 mm. For fine pitch, drill 22.0 mm. Smaller drills give more engagement but increase tap breakage risk without meaningful strength gain.
M24 clearance hole
For a clearance hole where the bolt passes through, use 25.0 mm (close fit), 26.0 mm (medium), or 28.0 mm (coarse) per ISO 273.
M24 torque values
Dry M24 property class 8.8: torque to 690 Nm. Class 10.9: 970 Nm. Class 12.9: 1140 Nm. These values target 90% proof load with K=0.20 dry thread friction. If threads are oiled or coated, reduce by 20-25%. For critical joints, always verify against the fastener manufacturer's datasheet.
M24 spanner and hex key
An M24 hex head bolt (ISO 4014) has 36.0 mm across flats, so you need a 36.0 mm spanner or socket. M24 socket head cap screws (ISO 4762) have 36.0 mm head diameter and need a 19.0 mm hex key (Allen key).
Related standards
- ISO 261 - ISO general-purpose metric screw threads
- ISO 273 - Fasteners: clearance holes for bolts and screws
- ISO 898-1 - Mechanical properties of carbon steel fasteners
- ISO 4014 - Hexagon head bolts, product grades A and B
- ISO 4762 - Hexagon socket head cap screws
- VDI 2230 - Systematic calculation of bolted joints
References
- ISO 261:1998 - ISO metric screw threads
- ISO 898-1:2013 - Mechanical properties of fasteners
- VDI 2230:2015 - Calculation of bolted joints
Frequently Asked Questions
What is the thread pitch of an M24 bolt?
A standard M24 bolt has a coarse thread pitch of 3.0 mm per ISO 261. The fine pitch version is M24 x 2.0. If a drawing says M24 with no pitch specified, it means M24 x 3.0 coarse.
What is the tap drill size for M24?
For M24 x 3.0 coarse pitch with 75% thread engagement, drill 21.0 mm. For fine pitch, drill 22.0 mm. These values give a good balance of thread strength and tapping ease.
What torque is an M24 bolt rated for?
For a dry M24 property class 8.8 bolt, the standard torque is 690 Nm. Class 10.9 takes 970 Nm, class 12.9 takes 1140 Nm. Values are per VDI 2230 at 90% proof load with nut factor K=0.20. Reduce by 20-25% if threads are lubricated.
What spanner size fits an M24 bolt?
An M24 hex head bolt (ISO 4014) has a 36.0 mm across-flats (A/F) dimension, so you need a 36.0 mm spanner or socket. An M24 socket head cap screw uses a 19.0 mm hex key (Allen key).