Perfect Fit has developed the first cock ring sizing system designed to fit you without too much pull but with enough restriction to be truly effective. We had to throw-away the sizing system that has become the de facto standard. We determined that we had to make rings that are only 0.1" (2.5mm) apart in sizing to get rings that would fit perfectly. The new rings are call Xact-Fit(TM). Now we make 14 Xact-Fit rings sizes where other manufacturers make only 3 to 5 sizes in this same range. Made of a plush soft touch silicone the Xact-Fit ring is premium quality and incredibly strong. Each Xact-Fit ring is stamped with its size so no more guessing! Stack the rings for additional fun. #21-2.1 inch diameter and 6.6 inch circumference.