They recognise coating used on wheel (4)
I believe the answer is:
tyre
'wheel' is the definition.
(I've seen this before)
'they recognise coating used on' is the wordplay.
I cannot really see how this works, but
'on' could be 're' ('on' can be mean 'with reference to') and 're' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for tyre that I've seen before include "Rubber ring on a wheel" , "Rubber surround on a wheel" , "Pneumatic device on wheel" , "A spare one round the middle is fat" , "Rubber wheel-ring" .)