Replacement radiator knobs

[uptodat]

The plastic knobs on the wheel valve and lockshield valves on all my rads are 25 years old and crumbling, meaning I have to use a wrench to turn rads off or adjust temp. Are eplacement knobs available anywhere? Failing that, is it possible to get a tool that justs sits over the spindle of the valves instead of a wrench? (These are round with two flatted sides.)
I'm told the plastic does "go off" over the years. Is this a ploy to make you buy new valves just because the knob has cracked or crumbled?

 

[BingoBongo]

of course it is a ploy

they want you to buy 2p knobs every 25 years

 

[mickyg]

http://www.holdfastradiatorvalves.co.uk/

 

[Freddie Orrell]

"a tool that justs sits over the spindle of the valves instead of a wrench" is a 3/8in-square-drive 'universal socket' 7mm-19mm. This is a socket filled with sprung pins to grip various sized nuts, the pins completely filling the aperture; the 9mm-21mm version with pins that leave gaps does NOT grip in this situation. Any combination of adaptor, handle and/or extension for 3/8in sockets can be used to drive it.