75 ,the "nominal size" (to start) was/is 7.225 on the Impeller skirt and 7.250 on the wear ring inner surface , different types and brand of wear rings are made in several "undersizes"/"oversizes" To obtain the correct US to keep .025 clearance (without machining yours) would require a .035 US w/ring ,likley custom (assuming I'm not to tired to do the math ) Call or PM if we can help Tom