radiator bleed nipple/valve

[gillsboy2010]

Hi I got a couple of rads that where the bleed nipples have rounded abit so cannot get a good fit with the bleed key, anybody know what size socket could be used to hopefully undo these little bliters and let me bleed them and hopefully get a replacement screw

 

[Elkato531]

The square hole in a rad key is often recessed slightly. I file the end down so that the hole is flush with the end of the key. This gives a much better purchase on dodgy bleed screws.