What is a universal radiator key?

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     Parts of a universal radiator key  
  Universal radiator key 3  

The parts of a universal radiator key are:


  • A tapered hexagonal shaft for use on internal hexagon valve tails

  • A tapered shaft with grooves for the fixing and removal of internally-lugged tail valves

  • A square end for fixing and removal of square section bleed plugs and blanking plugs

  • A hole to give clearance to bleed screws when removing square section bleed plugs

  • A sliding handle, often referred to as tommy bar

  • Ends caps at either end of the handle to prevent it falling out of its hole

  Universal radiator key  

The universal radiator key has three profiles. Profiles are the shapes that fit the valve tails and plugs that this key operates. The two main profiles either side of the handle are tapered and therefore self-restricting.


Self-restricting means that by pushing the tapered profile into the valve tail as far as it will go, it will fit valve tails of different sizes from 12mm to 14mm.

  Internal hex type radiator valve tail  

It will fit tails with internal hexagonal shapes that are straight or tapered…


Internally lugged radiator valve tail


…and what are known as bayonet, or internal lug type tails, allowing for variations in size.

  Square section bleed plub  

The third profile is the square end that fits square section bleed and blanking plugs.


This picture shows a square section bleed plug.

  Universal radiator key with adjustable handle  

The three profiles make the tool ‘universal’, which suggests it can be used for all tasks performed on a radiator.


However, the three profiles do not cover every operation. For instance, it cannot be used for bleeding radiators.


This particular spanner has an adjustable or ‘floating’ handle, called a tommy bar, which is useful when space is restricted.

   Universal radiator valve key  

Universal radiator keys are usually made from high tensile steel or case hardened steel.


High tensile steel is twice as strong as the mild steel used for some tools. Case hardened steel means the surface of the steel has been hardened, but the metal deeper inside remains softer. High tensile steel is stronger throughout.

   Universal radiator key with spanner  
  Universal key with spanner  

This is another type of ‘universal’ or multi-purpose radiator spanner. It performs all the same functions as the universal spanner above, and a bit more.


It includes an open-ended spanner which is ‘stepped’ to fit different radiator nuts including some bleed plugs and blanking plugs. It also incorporates a radiator bleed key.


However, it lacks an adjustable handle, so may not be as easy to use in restricted spaces.

  Jaws of universal radiator key and spanner      
  Various radiator valve keys  

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