Bb Clarinet Mouthpieces Boehm system Vandoren СМ4028 5RV Lyre "13 Series" with beak versions Profile 88. More open than the 5RV with a longer facing.
The “13 series” mouthpiece was developed specifically for American clarinetists using A440 pitch.
A=440. The Beak: Profile 88. Tip Opening: 109+ (1/100mm). Medium Facing. Works best with Vandoren #3-#4 Reeds.