Trumpet Bottom Cap Booster Rings Brass (Medium) Set of 3, Used. These are used by opening the bottom caps of your trumpet valves and inserting the rings inside, then tightening the caps. This creates a moderate resistance and 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 works best for you. (I always put the brass (medium) ring in the 3rd valve only.) These are used items, so they have some minor wear and tear. Therefore, I am offering them at a reduced price. If anyone is interested, please let me know. Thank you. m(_ _)m