The Circle Savvy Ruler is designed to work with most 45mm or smaller rotary cutters. Hold rotary cutter straight up and down for ease to cutting. Guide the rotary cutter along the inside edge. Cut circles, semi-circles, & quarter-circles from 3in to 15-1/2in and every 1/2in in between. So many options for a quick easy quilts, home deco projects so many options.