On listing is four pieces of silicone rubber ring tube damper. Tubes are always susceptible to microphonic effect. This tube damper minimize the tubes mechanical ringing and thus improves the sound. This tube damper is good for dimension of 9-pin tube such as 12AX7, 6DJ8 etc. We recommend to use two rings per one tube. Silicone rubber is an elastomer that can sustain high temperature up to 300 degree Celsius. We do air shipping worldwide at US$4.00.