Plastic Bed Frame Caster Insert Plugs, 1/2-Inch Outside Diameter, Set of 4 These plastic inserts are made to be inserted in your bed frame to allow the correct fit for your casters, rug rollers or wheels. These plastic insert plugs are packaged and sold as a set of 4. Made of high-strength, HDPE plastic. Height Including Flange: 1 13/16" , Stem Length: 1 9/16", Internal Diameter: 3/8" This item is manufactured in the United States.