Hi Simon, pot metal, specifically the tin and lead used in pot metal was prohibited for use other than for military during WWII. Sterling became the metal for costume jewelry of necessity.
White metal and rhinestone dress clips were especially popular during the 1930s. Fur clips were popular in the 1940s. Fur clips and be distinguished from dress clips because the pair of prongs on the fur clips have a sharp tip.
I think this piece of vintage jewelry is either a dress clip or a fur clip.
