Balance plates (6)
I believe the answer is:
scales
This clue is a double definition.
'balance' is the first definition.
(balance can mean a set of scales)
'plates' is the second definition.
(I know this)
(Other definitions for scales that I've seen before include "Zodiac sign < covering fish" , "Sequences of musical notes" , "Instruments for weighing things" , "Flakes of fish skin" , "Set of musical notes - balanced on a fish?" .)