Hexagonal profile for fixing or removing valve tails
Square profile for fixing or removing bleed plugs and blanking plugs
A hole to give clearance to bleed screws when fitting/removing bleed plugs
This is another type of multi-purpose key for working on radiator valve tails, bleed plugs (but not bleed screws) and blanking plugs. It fits the integral external nuts on some 1/2 inch radiator valve tails…
…the 1/2 inch square sections of some bleed plugs (as seen here) and some blanking plugs…
…and the internal hexagons of 1/2 inch valve tails.
This type of wrench is usually made of hardened steel for strentgh and durability.
For step-by-step guides to some of the things you can do with this key, see: How to bleed a radiator?