Schilke Symphony series trombone mouthpieces. The M5.1, M5.2 and M5.3 have medium shallow cups for players desiring more brilliance and projection. The D5.1, D5.2 and D5.3 mouthpieces have deeper cups, providing increased depth of sound. The * models have a more tapered throat which will feel more open and will have increased flexibility. The 6.0 models are improvements on the standard model 60 bass trombone mouthpieces.