M18 Bolt Size and Thread Specifications
What is an M18 bolt?
An M18 bolt has 18 mm nominal diameter with 2.5 mm coarse pitch commonly listed for ISO metric coarse. Fine pitches are used where drawings require them.
M18 serves very high-load joints in heavy machinery and large structural connections. Use torque specs and lubrication class appropriate to the bolt grade. Spanish reference: perno M18.
Specifications
| Specification | Value |
|---|---|
| Nominal diameter | 18 mm |
| Standard pitch (coarse) | 2.5 mm |
| Fine pitch | 2.0 mm |
| Tap drill size | 15.5 mm |
| Closest imperial equivalent | 3/4-10 |
Hex head size
| Bolt size | Hex head size |
|---|---|
| M18 | 27 mm |
Common uses
Heavy engineering, large spindles, flanges, and industrial equipment with high clamping requirements.
Related tools
Related charts
FAQ
What is the standard pitch for an M18 bolt?
The common coarse pitch for M18 is 2.5 mm. Fine pitch is often 2.0 mm where specified.
What drill size should be used for tapping M18 threads?
For M18 x 2.5 coarse thread, use approximately a 15.5 mm tap drill. Use our Tap Drill Calculator for other pitches.
What imperial fastener is closest to M18?
3/4-10 is a practical reference for comparing M18 to inch hardware; verify fit for your application.
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