This is a round stick of cork 1-1/2" long for use as a rotary valve stop. The cork is available in several diameters for use on any size brass instrument with rotary valves. Each stick should complete two rotors. It is easily cut to length with a small knife.
Most new instruments use some rubber or neoprene style material for the rotary valve stops. We also sell that material, called Round Rubber Stop. Though cork does not last as long as these synthetic materials, cork has several advantages. Cork is quieter and absorbs energy of the rotor impact better to reduce bouncing. If you're playing especially fast technical music, you want to reduce rotor bouncing on the upstroke. Cork stops may help improve this.