The Gen 2 28F is very similar in diameter and feel to a PT65. Wedge F tuba cups are similar to a PT65 cup. They have a shallow, modified V shape, which provides an excellent balance of clarity and projection with an even response in all registers and a round, full tone.
ID: 1.28 inches at .05 inches into the cup (32.51 mm)
OD: 1.88 inches (47.75 mm)
Throat: .310 inches (7.87 mm)