Pos-T-Vac Mach Ring Xlarge #8 - REPLACES URMACH1TENSIONRING8.Mach Ring 8 (XL) inside diameter 13.5mm (.550 inches).PosTVac Mach Ring has a thick center, creating an evenly dispersed tension and comfort over a wide area.The Mach Ring will maintain adequate firmness for approximately 30-40 uses. Latex Free.