- Undo nuts
- Undo bolts
- Hold a shaft still
- Don't buy cheap ones - the jaws wobble
- Padded handles are a good idea
If you’ve filed a head to an odd size and you aren’t using surface drive spanners this is the ultimate get out of jail free card… buy high quality if you can afford it as this will have less play in the adjustment mechanism so the jaws will stay rock solid.