Gem right inside ring (5)
I believe the answer is:
pearl
'gem' is the definition.
(pearl is a kind of gem)
'right inside ring' is the wordplay.
'right' becomes 'r' (common abbreviation).
'inside' indicates putting letters inside.
'ring' becomes 'peal' ('peal' can be a synonym of 'ring'**).
'r' going inside 'peal' is 'PEARL'.
(Other definitions for pearl that I've seen before include "Oyster's gem" , "Off-white colour" , "Lustrous globule prized as a gem" , "Drop" , "Object of great worth" .)