Increase stamina and endurance with the Size Matters Endurance Penis Ring Set. Complete with four differently sized rings. Made from stretchy TPR material that is both durable and long lasting. Simply select a ring and slide it over the shaft by grasping the tabs on the sides of the ring. Pull the ring back further and place behind the testicles. Now you are ready for a long and pleasurable ride! Size Rings Inner Diameter: .3 to .75 unstretched