The Denis Wick Trombone Mouthpieces in Silver offer the characteristics of clarity, warmth and beauty of sound with other mouthpiece makers strive to match. These mouthpieces are labeled so the first number refers to the cup diameter. The higher the number, the smaller the diameter.Cup Diameter: Model Number - the first number refers to the cup diameter--the higher the number, the smaller the diameter Cup Volume: A = Deep Cup; B = Medium Cup; C = Shallow Cup Rim: N = Narrow Rim Shank: L = Large Shank; S = Small Shank