Wheel-connecting rod (4)
I believe the answer is:
axle
'wheel-connecting rod' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for axle that I've seen before include "Rod making wheels turn" , "Pin in revolver" , "Shaft on which wheels rotate" , "Wheel rotates around it" , "Rotating spindle" .)