US grain producer's rights to import diamonds (5)
I believe the answer is:
ricer
'us grain producer's' is the definition.
(US term for a device which makes rice)
'rights to import diamonds' is the wordplay.
'rights' becomes 'rr' (two abbreviations for right).
'to import' means one lot of letters goes inside another.
'diamonds' becomes 'ice' (slang term for diamonds).
'rr' enclosing 'ice' is 'RICER'.
(Other definitions for ricer that I've seen before include "Sieve (US)" , "American kitchen utensil" .)