The CR91S doesn't really have a Bach inner diameter comparison, but if Bach made one, it would be around a Bach 14 inner diameter. Many people that have moved from the "Bobby Shew and Roger Ingram pieces, have gravitated towards this mouthpiece. This mouthpiece has a shallow V cup design with a Comfort Rim profile. This rim profile is a bit wider than all of the classical models, but not as wide and cushioned as the commercial models. All the inner diameter specs stay the same for each of the models, but the outer diameter increases on all of the classical models, and decreases on the commercial models. This mouthpiece has more resistance than the old Jet-tones providing more endurance, better projection and an easier high end. The sound is full and resonant from the very bottom of the range to the top. It has a 28 hole.

CR91S: 0.6309 inner diameter measured at 0.30" 0.1410 throat 28 drill