This listing is for one set of four SES brand polyurethane 5x1-1/4" Swivel Caster's (2 total locking swivel and 2 swivels) with a 1/2" hollow kingpin mounting rivet. This mounting allows you to use your own screw, bolt or any other type of specialty mounting as long as it is 1/2" in diameter or less. This set up is perfect for mounting casters to wood products using wood or lag screws and is also helpful when metric mounting is required.