Accurately Size Your Stones, From .03 Carats To 4 Carats; 2mm To 11mm. Aluminum, Revolving Gauge Has Birthstone Information On Back. Gauge Measures 3 5/8" X 2 3/4".* Measures: From .03 Ct To 4 Ct * 2mm To 11mm * Made Of Aluminum * Birthsone Info On The Back * Gauge Is 3 5/8" X 2 3/4"