Broad flat projecting rim (6)
I believe the answer is:
flange
'broad flat projecting rim' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for flange that I've seen before include "Flat outer face of rolled-steel joist" , "Rim (on wheel)" , "Broad flat projecting rim" , "Raised edge of a wheel" , "Projecting rim or piece" .)