M12 Bolt Specifications

26 April 2026

Verified by Rachel Mayfield, Supply Chain Analyst - April 2026

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

References

  1. ISO 261:1998 - ISO metric screw threads
  2. ISO 898-1:2013 - Mechanical properties of fasteners
  3. VDI 2230:2015 - Calculation of bolted joints

Where this data comes from: Supplier listings are verified against Companies House public records. Product specifications reference published ISO, BS, and DIN standards. Trade body data is sourced from official member directories.

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).

References