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". There is also a double loop variety when a wider range of suitable shafts is required. It also spreads out the stresses more evenly for a longer life. This type of pin is usually made of round wire of a harder metal than is appropriate for traditional cotter pins. DIN 11024 is example of standard that defines set of R-clips.