60mm (2-3/8" diameter) concave round. Moves everything as if it had wheels. Move up to 2500 lb. Won't scratch your floors. Works on any kind of surface: Wood floors, vinyl, ceramic tile, and carpeting. for casters or nonpermanent applications on footed furniture. For moving: Sofas, refrigerators, beds, tables, dressers, washers, dryers, and stoves. Will slide over doorsteps or floor edges with a height difference of up to 3/16". Color: Gray. As seen on TV.