Rubber O-Ring Oil Seal, Gasket, U-Ring, Quad-Ring, Glyd-Ring, Step Seal, Mechanical Seal, Extrusion Seals, Rotating Seals 1. All rubber products are made according to international standard: ISO 3601, AS 568A, DIN3771, JIS B2401.2. Our products are of NSF, WRAS, DVGW, FDA and ROHS approved.3. Various materials and hardness for your option, including Buna-N (NBR), HNBR, VITON, Silicone, ...