These mouthpieces have a medium cup depth similar to a Wick B cup
64 BRC
Inner Diameter: .640 measured .04 inches into the cup.
ID similar to a Wick 5B, with a wider, more comfortable rim.
65 BRC
Inner Diameter: .650 measured .04 inches into the cup.
ID between 4B and 5B, with a wider, more comfortable rim.
66 BRC
Inner Diameter: .660 measured .04 inches into the cup.
ID similar to the Wick 4B, with a wider, more comfortable rim.
67 BRC
Inner Diameter: .670 measured .04 inches into the cup.
ID similar to the Wick 2B, with a wider, more comfortable rim.
68 BRC
Inner Diameter: .680 measured .04 inches into the cup.
Larger ID than the Wick 2B, with a wider, more comfortable rim.