Drill part (3)
I believe the answer is:
bit
'drill part' is the definition.
('bit' is part of 'drill')
This is the entire clue.
(Other definitions for bit that I've seen before include "Between horse's teeth, this loses control" , "Cutting head of a drill" , "Piece; horse's restraint" , "scrap" , "Small piece - used teeth" .)