Comparing rim diameters between manufacturers is tricky. Manufacturers measure rim diameters at different points, which means you cannot directly compare measurements between manufacturers. Manufacturers who measure at a point closer to the crest of the rim report larger numbers than those who measure at a point deeper into the cup. As a result sizes can vary by as much as .01 inches for mouthpieces from different manufacturers with exactly the same size rim.
You should also remember that how a rim feels and performs is influenced my many factors other than the ID. Mouthpieces feel larger when they have a softer bite, a high point shifted away from the inside of the rim, and a wider rim from ID to OD. A very useful resource for comparing rim size and contour as well as cup depth is the Kanstul Mouthpiece Comparator. See table below for Wedge comparisons.
We measure mouthpieces from 12:00 to 6:00 (the long axis of the Wedge oval rim) at a point .04 inches below the crest of the rim. This is the most common place to measure, also used by Warburton and other makers. Below are some general guidelines that apply to most players with respect to rim ID of Wedge mouthpieces.
70 rim – .700 inches – Larger than practical for the vast majority of players. Comparable to a Schilke 24.
69 rim – .690 inches – Extra large ID, also larger than most players need. Works well with deep cups, but endurance is a challenge.
68 rim – .680 inches – Larger rim in the Bach 1 size range. Suitable for strong orchestral players using a deep or medium deep cup. Most players using a conventional rim of .680 or larger can easily adapt to a smaller 67 rim and gain range and endurance without any significant sacrifice of sound or flexibility.
67 rim – .670 inches – Our most popular size for professional players who need a mouthpiece in the Bach 1-1/2C to 1-1/4C rim size range. Works well with RT, D, MDV, and MD cups. Can be used with M cups. However, players needing an M or shallower cup for a brighter sound or for upper register support are often better served by using a slightly smaller 66 or 65 rim. Most popular mouthpieces in this range are 67MD and 67MDV (comparable to a Bach 1-1/2C).
66 rim – .660 inches – Our most versatile popular size for players who do not need the extra volume provided by the 67 rim. Works well with all cup depths from ES to RT. Being used by professional and amateur orchestral players and soloists with an MDV or MD cup, right through to concert band, pops, pit, and lead players of all levels. The 66 rim is also an excellent choice for piccolo trumpet when a player is using a 67 rim on their big horns. 66MV is a good substitute for a Bach 3C. 66MDV is similar to a Bach 5C.
65 rim – .650 inches – Very similar characteristics and applications to the 66 rim. An excellent choice for those seeking a little more efficiency, and for younger players with a developing embouchure. Especially popular size for piccolo, pit, pops, and lead with a medium or shallow cup. 65ES is a little larger than a Schilke 13A4A. Also works very well as in chamber orchestra or quintet with an MDV or RT cup when endurance is important and a dark sound is desired, but when if does not have to be as loud as in a large symphony orchestra. 65MDV is comparable to a Bach 7C.
64 rim – .640 inches – Smaller diameter more suitable for young players with an MD or MDV cup, or as a piccolo or lead mouthpiece with a shallower cup. 64ES is a little smaller than a Schilke 13A4A.
63 rim – .630 inches – Small diameter most suitable for lead trumpet with a shallow ES or S cup. 63ES is similar to a Schilke 6A4A.