Gem that’s right set in ring (5)
I believe the answer is:
pearl
'gem' is the definition.
(pearl is a kind of gem)
'right set in ring' is the wordplay.
'right' becomes 'r' (common abbreviation).
'set in' is an insertion indicator.
'ring' becomes 'peal' ('peal' can be a synonym of 'ring'**).
'r' going inside 'peal' is 'PEARL'.
'that's' is the link.
(Other definitions for pearl that I've seen before include "Precious jewel from the oyster" , "finest example" , "Lustrous globule prized as a gem" , "greatly valued" , "Small type" .)