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Every dimension, torque value, and thread specification for the M12 metric bolt in one reference card. M12 Bolt Specifications M12 is one of the most common metric fastener sizes in UK engineering, used across general machine assembly, motor brackets and structural fixings.
| Property |
Value |
Standard |
| Nominal diameter |
12.0 mm |
ISO 261 |
| Coarse pitch |
1.75 mm |
ISO 261 |
| Fine pitch |
1.5 / 1.25 mm |
ISO 261 |
| Tap drill (coarse, 75% engagement) |
10.2 mm |
ISO 2306 |
| Tap drill (fine) |
10.5 / 10.75 mm |
ISO 2306 |
| Clearance hole - close |
13.0 mm |
ISO 273 |
| Clearance hole - medium |
13.5 mm |
ISO 273 |
| Clearance hole - coarse |
14.5 mm |
ISO 273 |
| Hex head A/F (spanner size) |
18.0 mm |
ISO 4014 |
| Hex head height |
7.5 mm |
ISO 4014 |
| Socket head cap screw head dia |
18.0 mm |
ISO 4762 |
| Socket head hex key size |
10.0 mm |
ISO 4762 |
| Tensile stress area |
84.3 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 |
48.9 kN |
ISO 898-1 |
| Proof load 10.9 |
70.0 kN |
ISO 898-1 |
| Torque dry, class 8.8 |
85 Nm |
VDI 2230 |
| Torque dry, class 10.9 |
120 Nm |
VDI 2230 |
| Torque dry, class 12.9 |
140 Nm |
VDI 2230 |
M12 thread pitch
Standard M12 bolts use a 1.75 mm coarse pitch. Fine pitch M12 x 1.5 is used where vibration resistance matters or in thin-wall components. Coarse pitch is the default - if a drawing says M12 with no pitch specified, it means M12 x 1.75 coarse.
M12 tap drill size
For M12 x 1.75 coarse pitch with 75% thread engagement, drill 10.2 mm. For fine pitch, drill 10.5 / 10.75 mm. Smaller drills give more engagement but increase tap breakage risk without meaningful strength gain.
M12 clearance hole
For a clearance hole where the bolt passes through, use 13.0 mm (close fit), 13.5 mm (medium), or 14.5 mm (coarse) per ISO 273.
M12 torque values
Dry M12 property class 8.8: torque to 85 Nm. Class 10.9: 120 Nm. Class 12.9: 140 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.
M12 spanner and hex key
An M12 hex head bolt (ISO 4014) has 18.0 mm across flats, so you need a 18.0 mm spanner or socket. M12 socket head cap screws (ISO 4762) have 18.0 mm head diameter and need a 10.0 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
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Frequently Asked Questions
What is the thread pitch of an M12 bolt?
A standard M12 bolt has a coarse thread pitch of 1.75 mm per ISO 261. The fine pitch version is M12 x 1.5 / 1.25. If a drawing says M12 with no pitch specified, it means M12 x 1.75 coarse.
What is the tap drill size for M12?
For M12 x 1.75 coarse pitch with 75% thread engagement, drill 10.2 mm. For fine pitch, drill 10.5 / 10.75 mm. These values give a good balance of thread strength and tapping ease.
What torque is an M12 bolt rated for?
For a dry M12 property class 8.8 bolt, the standard torque is 85 Nm. Class 10.9 takes 120 Nm, class 12.9 takes 140 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 M12 bolt?
An M12 hex head bolt (ISO 4014) has a 18.0 mm across-flats (A/F) dimension, so you need a 18.0 mm spanner or socket. An M12 socket head cap screw uses a 10.0 mm hex key (Allen key).
What is the M12 standard pitch?
The M12 standard pitch is 1.75 mm, the coarse thread defined by ISO 261. If a drawing states M12 with no pitch given, it means M12 x 1.75 coarse by default. Fine pitch versions of M12 x 1.5 or 1.25 mm exist for vibration resistance or thin-wall components, but the 1.75 mm coarse pitch is the standard off-the-shelf option in UK engineering.
What is the M12 thread pitch?
The M12 thread pitch is 1.75 mm for the standard coarse thread under ISO 261. Fine pitch alternatives are M12 x 1.5 and M12 x 1.25 mm. Pitch is the distance between adjacent thread crests. For tapping an M12 x 1.75 coarse thread at 75% engagement, drill 10.2 mm; fine pitch threads use a 10.5 or 10.75 mm tap drill per ISO 2306.
What is the M12 bolt size in mm?
An M12 bolt has a nominal diameter of 12.0 mm and a 1.75 mm coarse pitch under ISO 261. The hex head measures 18.0 mm across flats with a 7.5 mm height per ISO 4014, so it needs an 18 mm spanner. The clearance hole is 13.0 mm close fit per ISO 273, and the tensile stress area is 84.3 mm per ISO 898-1.
What are the full M12 bolt dimensions?
An M12 bolt has a 12.0 mm nominal diameter and 1.75 mm coarse pitch per ISO 261. The hex head is 18.0 mm across flats with a 7.5 mm height under ISO 4014. Clearance holes are 13.0 mm close, 13.5 mm medium or 14.5 mm coarse per ISO 273. Tensile stress area is 84.3 mm and dry torque at class 8.8 is 85 Nm per ISO 898-1 and VDI 2230.