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What is an allen or hex radiator key?

What is an allen or hex radiator key?

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Parts of an Allen or hex radiator key
Allen or hex radiator key The parts of an Allen or hex key are:

  • Handle
  • End for fitting/removing internal hexagonal valve tails
  • Groove for fitting/removing valve tails with internal a lugs
  • Short end with square profile for fitting/removing bleed plugs and blanking plugs
  • Hole in square profile to give clearance to bleed screws when working with bleed plugs
Radiator and valve key half-inch section An Allen (sometimes called hexagon or hex) radiator key is for fitting and removing standard 1/2 inch radiator valves. It is also known as a half-inch section key.

This key is normally made from high tensile steel and is usually galvanised or zinc-coated for protection against corrosion.

Square section bleed plug It also has a square end for the fitting and removal of square section radiator plugs.

Square section means the plug has a square recess that the key will fit into for undoing and tightening.

Grooved end of Allen or hex key One end of this key is usually grooved to fit what are known as internally lugged valve tails.
Radiator plug end of an Allen or hex key The other, square, end is for for 3/8 inch (10 mm) square section radiator vent plugs (the plug which has a bleed screw in the middle), and blanking plugs with the same square recess.

There is a round hole in the end of the square head that gives clearance for the air vent screw, so the plug can be removed without damaging the screw.

For step-by-step guides to using this and some other keys, see  How to bleed a radiator and  How to fit and remove valve tails

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