Woodi Hardwood Piano Caster Cups WPA-10 Set of 4 Wood Unfinished 4" Designed for use with pianos Made of High-Quality Select hardwood, 4 cups in 1 package. Protects wood, tile, and carpet from piano caster damage Dimensions: 4" - outside diameter, 1.75"- inside diameter Underside of each cup is lined with felt pad