A butterfly spring is a thin, flexible strip of metal soldered to the inside bottom shank of a ring. Its purpose is to hold a ring securely on a finger and in an upright position.
Purpose of Butterfly Springs
Butterfly springs are useful for women whose knuckles are larger than the rest of her fingers. The device allows a ring to be sized slightly larger so that it can slip over the knuckle, yet be safe from twirling or falling off the finger.