The silver (or nickel, or gold...) rings are not only an embellishment to the pipe but they serve to reinforce the shank avoiding cracks on removing and assembling the mouthpiece.
So, they have to adjust perfecly to the shank. No tolerance here.
It isn't normal but a quick fix is to paint the shank with clear nail polish and slip the mount back on. Peterson's uses wood glue (Elmers). Many years ago they uised fish glue. If you go that route, the mount cannot be removed without destroying it.