Recommended replacement pop in style amp caster by the musicians on the Service Caster staff. Listing is for set of 4 High Quality Polyurethane Tread Amp Casters with Round Plate Sockets by Service Caster. This durable 2" wheel is safe for all floors and roadworthy, an upgrade from the standard 2" soft rubber caster wheels. Easy rolling with ball bearing swivel. Features easy to install round plate sockets with 4 1/4" screw holes for wood screws or machine screws with washer and nut (screws not provided). Hole required for socket is 9/16" wide by 1-1/2" deep.Fits most major brands using pop in stems (7/16" x 7/8").Safe for most floors, non-marking and non-marring.