Box of various parts (4)
I believe the answer is:
spar
'box' is the definition.
(sparring is a kind of boxing)
'of various parts' is the wordplay.
'of' says the answer is hidden in the clue.
'SPAR' can be found hidden inside 'various parts'.
(Other definitions for spar that I've seen before include "Mineral; strong pole" , "Translucent mineral" , "Scrap" , "dispute" , "Wooden pole -- box" .)