A Stainless Steel Cotter Pin or Sometimes Called Split Pins or Cotter Keys, are a Bent Pin With a Rounded Head That are Made to Fit a Specific Size Hole. Once in The Hole The Split Pin is Bent To Lock In the Bolt, Castle Nut Or Rod. Our Stainless Steel Cotter Split Pins Come in a Varity of Diameters and Lengths. Made Out of 18-8 / 304 Grade Stainless Steel.