Bar in a limo (4)
I believe the answer is:
axle
'bar in a limo' 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 attachment to wheels" , "Shaft with wheels attached" , "Shaft on which wheels rotate" , "Metal pin on which wheel revolves" , "Spindle between wheels" .)