These High-Impact Plastic Piano Caster Cups are designed by CPS Imports to be placed under a piano"s legs in order to protect floors and carpets. Caster cups are critical in the protection of hardwood floors, carpets, tile, and other flooring materials. Made of High-Impact Plastic. Dimensions: 4" - outside diameter, 2" - inside diameter. Available in Ebony color. Listing is for 4 caster cups.