What size spanner or socket does a 1/2" bolt take?
Answer
A 1/2" hex bolt takes 3/4 in across the flats — spanner or socket, and the same for its nut. A socket-head cap screw of the same size takes 3/8 in.
How it is worked out
- Spanner / socket — across the flats of the head
1/2" → 3/4 in - Hex (Allen) key — socket-head cap screw
1/2" → 3/8 in - The nut takes the same spanner
3/4 in fits the 1/2" 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)
- 3/4 in
- Socket size
- The same as the spanner — 3/4 in.
- Hex (Allen) key
- 3/8 in for a socket-head cap screw of this thread.
- The nut
- A standard 1/2" hex nut takes the same 3/4 in.
- 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
The rest of the job at this size
Do it with your own numbers
This page answers one specific question. The Tap Drill & Thread Size Calculator takes any values you like and answers as you type — in your browser, so nothing you enter is sent anywhere.