12B - 

Body Nickel Plated Copper Alloy, Hole Diameter 0.437 in., Phone Jack

Mate with standard 0.25" (6.35 mm) or 0.21" (5.33 mm) phone plugs. Notched insulating washers. Mounts in single 0.375" (9.52 mm) hole, panels up to 0.156" (3.96 mm) thick, except Types L-11 and L-12A in panels up to 0.25" (6.35 mm) thick.