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Cotter pins, also referred to as split pins or cotter keys, are fasteners used to secure other cylindrical shaped fasteners such as clevis pins in place. They are typically made from U-shaped pieces of thick wires mat may come in straight or hairpin variations. Traditional or straight cotter pins have two parallel lines used in shafts or clevis pins and are normally bent upon installation. Hairpin cotter pins also called retaining clips, R-clips, R-pins, or R-keys, have a pin design ideal for grooved assemblies.