Conn Precision 4 vs Kelly 3C
The Kelly 3C has a wider cup diameter, the Kelly 3C features a deeper cup.
Cup Diameter
The Kelly 3C has a cup diameter of 17.02 mm compared to 16.41 mm on the Conn Precision 4 — a difference of +0.61 mm. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
The Kelly 3C has a very deep cup while the Conn Precision 4 has a medium cup. Deeper cups favor a darker, richer sound; shallower cups provide more brightness and easier upper register.
Material
The Conn Precision 4 is described as Silver-plated brass, and the Kelly 3C as Lexan polycarbonate. Material affects mass, warmth, and how quickly the piece responds.
Which is better?
Both mouthpieces are categorized as "General" — the physical dimensions above will determine which suits your embouchure and playing style better.