Flip over how big an accessory is? (7)
I believe the answer is:
capsize
'flip over' is the definition.
(I've seen this in another clue)
I cannot understand how the rest of the clue works.
(Other definitions for capsize that I've seen before include "Of boat, turn turtle" , "Overturn (a boat)" , "Upset" , "Turn so that keel faces upwards" .)