These mouthpieces feature more than double the outside mass compared to standard Bach mouthpieces. The added mass darkens the sound and allows you to play at higher dynamic levels without distortion. They slot well, so the pitch centers dependably and the slightly larger throat offers less resistance, greater flexibility, and a warmer, more powerful sound that works well for concert or jazz. The Bach mouthpiece numbering system is arranged in an orderly progression from the largest to smallest diameters numbered from low to high.