Bach 3 vs Bach 6½A (small shank)
The Bach 3 has a wider cup diameter.
Mouthpiece A
Bach 3
• Baritone / Euphonium
Cup diameter26.26 mm / 1.0339 in
Cup depthDeep
Rim width—
Throat diameter5.85 mm / 0.2303 in
Backbore—
Finish—
Material—
Best suited for
Orchestral playing — large cup for full, dark tone
High-volume projection — open throat for power
vs
Mouthpiece B
Bach 6½A (small shank)
• Baritone / Euphonium
Cup diameter25.40 mm / 1.0000 in
Cup depthDeep
Rim width—
Throat diameter5.85 mm / 0.2303 in
Backbore—
Finish—
Material—
Best suited for
Orchestral playing — large cup for full, dark tone
High-volume projection — open throat for power
Cup Diameter
The Bach 3 has a cup diameter of 26.26 mm / 1.0339 in compared to 25.40 mm / 1.0000 in on the Bach 6½A (small shank) — a difference of 0.86 mm / 0.0339 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
Both mouthpieces share a deep cup depth, so the sound character from depth alone will be very similar.
Throat Diameter
Throat diameters are essentially identical at 5.85 mm / 0.2303 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.