Bach 10½C Flugel vs Bach 5B Flugel
The Bach 5B Flugel has a wider cup diameter, the Bach 5B Flugel features a deeper cup.
Cup Diameter
The Bach 5B Flugel has a cup diameter of 16.25 mm / 0.6398 in compared to 15.90 mm / 0.6260 in on the Bach 10½C Flugel — a difference of 0.35 mm / 0.0138 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
The Bach 5B Flugel has a deep cup while the Bach 10½C Flugel has a medium cup. Deeper cups favor a darker, richer sound; shallower cups provide more brightness and easier upper register.
Throat Diameter
Throat diameters are essentially identical at 3.99 mm / 0.1571 in, so resistance feel will be comparable.
Which is better?
Neither mouthpiece clearly dominates the other — the right choice depends on your embouchure, playing style, and the sound you're after. Try both if possible.