Outer cup diameter: 5 ¼”, inner cup diameter: 2 ¾” Slip under each leg of your grand piano to protect your floors from marks and scratching and your carpet from damage Work as well on wood and tile floors as on carpets Strongest-in-the-market reinforced ABS plastic construction. Smooth, snag-free, scratch-free base design that evenly distributes the weight of the piano over the cup’s circumference Almost right-angled lip prevents wheel from rolling out of cup 3-Pack high quality, heavy duty ebony grand piano Caster Cups. May also be used for other large and heavy furniture provided that their legs fit into the inner diameter of the cups. Satisfaction guaranteed.