Bar that fits into the notches of a toothed wheel (7)
I believe the answer is:
ratchet
'bar that fits into the notches of a toothed wheel' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for ratchet that I've seen before include "Bar to fit the notches of a toothed wheel" , "Device allowing motion in one direction only" , "Device preventing turning backwards" , "Toothed rack" , "Set of teeth" .)