The opening for each size on the template is created by using U.S. standardized diameters. We offer both a whole size and half size template. The one marked Half Size gives the correct in between size for the number shown, i.e. a 7 by the opening means 7 1/2.
Keep in mind that if you are creating ring shanks with wider bands that even though the ring size you measure for would be of the technically correct diameter you should make the finished size slightly larger by perhaps a 1/4 size to allow for the width that will be greater than the thickness of these templates. The ultimate solution for perfect sizing is to create your ring the standard two sizes larger and utilize a HattieS® Patty to control shrinkage to the final size you choose.