These metal ring size testers have 4 size ranges; U.S. sizes 1-15, millimeter sizes 13-24.2, international sizes 1-36, and CU sizes 41-76. Note: There may be variations between our ring sticks and ring sizers. US sizes are marked in whole, half ( - ) and 3/4 ( = ) increments. Except the last size which is size 15.