Features: 1.Every product has a unique Manufacturing Part Number label on the inner package that proves it has been qualified,which include Part Number,Model Number and inspection date information; 2.If you have any questions about the item,please provide us the Manufacturing Part Number for checking,your profits will be guaranteed. 3. High quality material: choose high quality metal and plastic, suitable for long-term use. 4. Wide application: suitable for three-tone B-flat trumpet / cornet / B-flat trumpet. 5. Durable: the spring shrinks with tension, the strength is good, and the positioning is accurate and the coaxiality is guaranteed, and the hand feels good. .