This is a vintage  petite necklace shortener or accessory made of three Japanese saltwater akoya cultured pearls. It comes on the original mid-century packaging.

The the pearls are lustrous with rosy overtones. They measure 4.00mm. 

Measures 3/4 inch. It is petite. Not stamped but tested and guaranteed solid solid sterling. From mid-century. It is not a sharp pin for clothing but clips over a strand of pearls as an accessory or to shorten it. 

All pearls are truly vintage and have only been lightly cleaned.