Trumpet Bottom Cap Booster Rings Brass (Thin) Set of 3, Used. These are used by opening the bottom caps of your trumpet valves and inserting the rings. Tightening the cap creates a moderate resistance, which is said to improve the tone. Some people use all three rings, while others only use one in a specific valve. Since results vary depending on the instrument and the individual, experiment with different combinations to find the number and placement that suits you best. (I always use the brass (medium) ring in the 3rd valve.) These are used items and therefore slightly dirty. That's why I'm offering them at a low price. If anyone is interested, please let me know. Thank you. m(_ _)m