Set of 2 black rubber waterkey pads (spit valve corks). Although commonly called "corks," these are synthetic—there is no cork in the composition. Useable on most brass instruments from trumpet to tuba. Peel and stick backing makes for easy installation and does not require the use of glue, pad cement or heated shellac. Set contains two pieces, each 4.2mm thick by 9.5mm (3/8-inch) in diameter. This medium size will fit most popular brass instruments.