Perfect Fit Xact Fit #18 2 Pack Black Cock Rings from Perfect Fit Brand. Imagine if a finger ring only came in three sizes equivalent to the circumference of a dime and a quarter and a dollar coin, how would they fit? Well until now, cock rings were sized even farther apart than this! No wonder finding a good fitting cock ring is near impossible. 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 inch apart in sizing to get rings that would fit perfectly