Cup diameter, mouthpiece

In cases where the edge between the rim and the cup (the bite) is sharp, the cup diameter of a mouthpiece is the diameter of this sharp edge; in cases where the edge between the rim and the cup is rounded, the cup diameter can most usefully denote the diameter of the cup at a depth from the plane of the furthermost part of the rim contour of the radius of the bite; this is usually equivalent to the diameter at the point of maximum curvature of the bore profile between the rim and the cup, and corresponds well with the measurements given by manufacturers of mouthpieces