A2 Stainless Steel UNF Half Thin Lock Locking Nuts 1/4" 5/16,3/8, 7/16, 5/8,3/4"

UNF Hexagon Half Nuts. UNF thread half nuts. A2 Stainless Steel. Nut thickness is half the size of a standard nut and often used as a locking nut. 3/8" x 24tpi.

eBay