This is a Brite Gold Dome Shape 1/2 Ball  Lightweight 'stamped" (hollow) Metal Button with Engraved Pattern shank base.

Sizes:

15mm (5/8" or 24/L)

18mm (11/16"-28/L)

20mm (3/4" or 30/L)

23mm (7/8"-36/L)

25mm (1" or 40/L)