What size spanner or socket does an M30 bolt take?

Answer 46 mm

An M30 hex bolt takes 46 mm across the flats — spanner or socket, and the same for its nut. A socket-head cap screw of the same size takes 22 mm.

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How it is worked out

Spanner / socket — across the flats of the headM30 → 46 mm
Hex (Allen) key — socket-head cap screwM30 → 22 mm
The nut takes the same spanner46 mm fits the M30 hex nut too

A standard hex is about 1.5x the thread diameter across the flats; the exact figure is fixed by the standard, not the formula

Worth knowing

Spanner size (across flats): 46 mm
Socket size: The same as the spanner — 46 mm.
Hex (Allen) key: 22 mm for a socket-head cap screw of this thread.
The nut: A standard M30 hex nut takes the same 46 mm.
This is the head, not the thread: The spanner fits the head. What the bolt threads into is the tap drill, and how hard to do it up is the torque — both linked below.

Spanner and socket size — nearby sizes

M2741 mm M2436 mm M2234 mm M2030 mm M1827 mm M1624 mm M1421 mm M1218 mm M1016 mm M813 mm

The rest of the job at this size

Tap drill for M30 × 3.526.5 mm Tightening torque for M30 × 3.5every grade

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