Cotter pins, or split pins, are two-pronged, metal fasteners. You line up the holes in two or more objects that you want to connect, insert the prongs through the holes and bend the prongs apart to secure the objects. Cotter pins can be made of steel, nickel, copper, brass, bronze or aluminum. Multiple types are produced.
Chisel point cotter pins have pointed prong ends. They are made in two varieties: "extended prong," in which one prong is longer than the other, and "even end," in which the prongs are the same length.
Taper point cotter pins have rounded prong ends. They also are made in "extended prong" and "even end" varieties.
Hammerlock cotter pins have one prong that is longer than the other and curves over the end of the other prong. When you hit the pin with a hammer, the shorter prong moves forward, forcing the prongs apart and locking them into place.
Clinch cotter pins have a large head and a curve in one of the prongs. The prongs spring apart automatically when you insert them.
Hairpin cotter pins are also called R-clips because they are shaped like the capital letter "R." You insert the straight prong into a hole near the end of an axle or other shaft, and the bent prong grips the shaft.