Bolt Size Helper

Quick lookup for metric & imperial bolt sizes and spanner/socket sizes.

Metric Bolt Size

Example: M6, M8, M10, M12…

Metric thread (e.g. M8)

Bolt size (metric) –

Approx diameter (inch) –

Spanner / socket size –

Example: 1/4", 5/16", 3/8", 1/2"…

Imperial bolt size (fraction, e.g. 3/8")

Nearest metric thread –

Bolt diameter (inch) –

Spanner / socket size (inch) –

Spanner / socket size (mm) –