Fit of rims on underparts:

Standard-width underparts have an inner diameter of .655 inch, or 16,6mm. This is where the two parts fit together, NOT the rim's inner diameter, where the embouchure contacts.                                                                                                                             

"Wide-width" underparts have an inner diameter of .670 inch, or 17mm. This additional width allows for a wider ID where the embouchure contacts.                                      

Even wider underparts diameters are available, as for the Paxman Halstead-Chidell rims.                                                                                                                     

Below are a few macro photos showing an underpart being measured, and the inner rim diameter being measured. (1) This mouthpiece underpart being measured has a "join" diameter of .675 inch ("Wide"). (2) The rim shown happens to have an inner diameter of 18mm, as shown by the gauge.

     Gauge bottom  (.675")

  Gauge in place                                                            

Rim and inner rim edge gauge

    Inner rim edge gauge in place (18mm)                                                                                            

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