What wrench fits a M8 bolt?

Across-flats wrench/socket size by head type - a flange bolt often uses a smaller wrench than a standard hex bolt of the same diameter, so always check the head type.

System

Bolt size

Nominal diameter	8 mm
Standard hex	13 mm
Hex flange	13 mm
Recommended clearance hole (medium fit)	9 mm
≈	≈ 1/2" (5/16")

Reference values only - always verify against the actual part before machining, tapping or tightening anything.