Premium SBR Rubber Piano Caster Cups - Black Premium Quality SBR (styrene-butadiene rubber) Grand Piano Caster Cups. Concert / stage quality casters secure the grand piano in place while keeping the casters from marring or scratching the floor. Large, stepped footprint with thick felt bottom pad distributes weight and protects fragile flooring. SBR rubber acts as a damper between piano and floor allowing for pure sound intonation. Premium SBR rubber does not promote tarnishing of brass. Premium SBR Mix Big, 6" Footprint with Stepped Design, Thick Felt Bottom Pad Sound Dampening Rubber Sold as a pack of 3 cups