One part in a brace, perhaps (3)
I believe the answer is:
bit
'one part' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for bit that I've seen before include "chip?" , "Segment" , "'Part, fragment (3)'" , "gripped" , "Small portion - part of drill" .)