split cotter
spring cotter

There are signs that manufacturers and stockists are increasingly listing both names together to avoid confusion; this led to the term split cotter sometimes being used for a split pin.

An R-clip, also known as an R-pin, R-key, hairpin cotter pin, hairpin cotter, bridge pin, hitch pin or spring cotter pin, is a fastener made of a springy material, commonly hardened metal wire, resembling the shape of the letter "R".