Diamond figures (6)
I believe the answer is:
carats
'diamond figures' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for carats that I've seen before include "Jewellers measure" , "Units of weight of precious stones" , "Weights of gold" , "They're used to measure gems and express purity of gold" , "Units of weight of diamonds" .)