Pos-T-Vac Ultimate ll Round Ring Size 4 - REPLACES URULTIMATEIIRNDRING4.Ultimate Round Ring 4 (XL) inside diameter 16mm (.63 inches).PosTVac Ultimate Round Ring is soft and pliable, offering even and lasting tension for approximately 20-30 uses.Rings are latex-free and should be replaced every 3-6 months depending on the frequency of use.