M16 Bolt Specifications

26 April 2026

Verified by Rachel Mayfield, Supply Chain Analyst - April 2026

Every dimension, torque value, and thread specification for the M16 metric bolt in one reference card. M16 Bolt Specifications M16 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 16.0 mm ISO 261
Coarse pitch 2.0 mm ISO 261
Fine pitch 1.5 mm ISO 261
Tap drill (coarse, 75% engagement) 14.0 mm ISO 2306
Tap drill (fine) 14.5 mm ISO 2306
Clearance hole - close 17.0 mm ISO 273
Clearance hole - medium 17.5 mm ISO 273
Clearance hole - coarse 18.5 mm ISO 273
Hex head A/F (spanner size) 24.0 mm ISO 4014
Hex head height 10.0 mm ISO 4014
Socket head cap screw head dia 24.0 mm ISO 4762
Socket head hex key size 14.0 mm ISO 4762
Tensile stress area 157 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 91.1 kN ISO 898-1
Proof load 10.9 130.3 kN ISO 898-1
Torque dry, class 8.8 210 Nm VDI 2230
Torque dry, class 10.9 295 Nm VDI 2230
Torque dry, class 12.9 345 Nm VDI 2230

M16 thread pitch

Standard M16 bolts use a 2.0 mm coarse pitch. Fine pitch M16 x 1.5 is used where vibration resistance matters or in thin-wall components. Coarse pitch is the default - if a drawing says M16 with no pitch specified, it means M16 x 2.0 coarse.

M16 tap drill size

For M16 x 2.0 coarse pitch with 75% thread engagement, drill 14.0 mm. For fine pitch, drill 14.5 mm. Smaller drills give more engagement but increase tap breakage risk without meaningful strength gain.

M16 clearance hole

For a clearance hole where the bolt passes through, use 17.0 mm (close fit), 17.5 mm (medium), or 18.5 mm (coarse) per ISO 273.

M16 torque values

Dry M16 property class 8.8: torque to 210 Nm. Class 10.9: 295 Nm. Class 12.9: 345 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.

M16 spanner and hex key

An M16 hex head bolt (ISO 4014) has 24.0 mm across flats, so you need a 24.0 mm spanner or socket. M16 socket head cap screws (ISO 4762) have 24.0 mm head diameter and need a 14.0 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 M16 bolt?

A standard M16 bolt has a coarse thread pitch of 2.0 mm per ISO 261. The fine pitch version is M16 x 1.5. If a drawing says M16 with no pitch specified, it means M16 x 2.0 coarse.

What is the tap drill size for M16?

For M16 x 2.0 coarse pitch with 75% thread engagement, drill 14.0 mm. For fine pitch, drill 14.5 mm. These values give a good balance of thread strength and tapping ease.

What torque is an M16 bolt rated for?

For a dry M16 property class 8.8 bolt, the standard torque is 210 Nm. Class 10.9 takes 295 Nm, class 12.9 takes 345 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 M16 bolt?

An M16 hex head bolt (ISO 4014) has a 24.0 mm across-flats (A/F) dimension, so you need a 24.0 mm spanner or socket. An M16 socket head cap screw uses a 14.0 mm hex key (Allen key).

References