Main design for plates (6)
I believe the answer is:
staple
'main' is the definition.
(I've seen this before)
'design for plates' is the wordplay.
'design for' is an anagram indicator (I've seen 'designed for' mean this (letters re-designed)).
'plates' is an anagram of 'STAPLE'.
(Other definitions for staple that I've seen before include "important things to eat" , "Paper fastening" , "Short U-shaped paper fastener" , "e.g. rice, sweetcorn ..." , "standard" .)