Buna-N (synthetic rubber) stop material in sizes to fit all brass instruments. Not affected by oil, grease, or solvents. When properly installed it will not bounce, compress, or tear. Unlike silicone, buna won't break down in use. Use .210" for Paxman, E. Schmid, Holton, Yamaha, and most other horns and trombones. Offered in standard 50 duro and extra-soft 40 duro. (40 duro is no longer being made.) Our .188 stock fits modern Conns, usually with no trimming. Available in 70 duro only. The Holton-Farkas (Omega-style) cord is available only in the 70 duro only. Some older Alexander horns need .250 for the change valve. Sizes .250"-.313" fits most tubas. Sold in six inch lengths. 

Tip: Buna is easy to trim using a sharp single edge razor blade. We often use two or three blades to install a set of bumpers.