Bolt Size Converter

Convert metric bolt sizes (M3–M24) to inches and nearest imperial equivalents.

Metric size:

–Inches

–Nearest fraction

–Spanner (mm)

How to use

Pick a metric size — inch decimal, fraction and spanner size appear; everything runs in your browser.

What size is an M8 bolt?

8 mm diameter — about 5/16 inch.

Does this include thread pitch?

Diameter only — pitch (e.g. M8×1.25) varies by coarse/fine thread standard.

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