Set of 3 High Quality&nbsp;Heavy Duty Ebony / Black Grand Piano / Furniture Caster Cups Outer cup diameter: 5 , inner cup diameter: 2 Slip under eachlegof 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 cups circumference Almost right-angled lip prevents wheel from rolling out of cup