Furniture Caster Cups,Jinli ABS Plastic Piano Caster Furniture Round Wheel Cups Piano non-slip mat Gripper Set Load Bearing for Upright Piano [4 Pack] Designed for use with grand pianos Protects wood, tile, and carpet from piano caster damage Designed to be placed under a piano's legs in order to protect floors and carpets Made for High-Quality ABS Plastic Material. Package : set of 4.