Drill attachment (3)
I believe the answer is:
bit
'drill attachment' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for bit that I've seen before include "Small piece; boring tool" , "Boring tip of a drill" , "Unit of information" , "Cutting piece of a drill (3)" , "The boring-piece of a drill" .)