Our Style PSU piston seal, or uniring, is a laminated one piece double acting seal made of cast polyurethane. The tough outer layer is highly resistant to abrasion and is impregnated with molybdenum disulfide to reduce friction. The softer inner layer acts as a static seal and also energizes the OD to make full contact with the bore. This seal may be used to replace an existing Uniring or other seals of the same dimensions - O-rings, O-rings with back-ups, T-seals, U-seals, etc. NOTE: Piston diameter "I" dimensions are given for pistons without wear rings.