Schilke 40B vs Schilke 42
The Schilke 42 has a wider cup diameter, the Schilke 42 features a deeper cup.
Cup Diameter
The Schilke 42 has a cup diameter of 23.22 mm / 0.9142 in compared to 22.51 mm / 0.8862 in on the Schilke 40B — a difference of 0.71 mm / 0.0280 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
The Schilke 42 has a medium cup while the Schilke 40B has a shallow 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 5.95 mm / 0.2343 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.