Appropriate part of harness (7)
I believe the answer is:
snaffle
I believe this clue is a double definition.
'appropriate' is the first definition.
(I've seen this before)
'harness' is the second definition.
(thesaurus)
'part of' is the link.
(Other definitions for snaffle that I've seen before include "Appropriate" , "Capture" , "Pinch" , "bit for the horse" , "Get hold of" .)