The materials used as O-rings are nitrile rubber, carboxylic acid nitrile, fluorine rubber, ethylene propylene, hydrogenated NBR, silicone rubber, neoprene rubber, fluorine silicone rubber, polyurethane, chlorine alcohol, butadiene, butyl rubber, natural rubber, ethylene/propionic acid rubber, polyacrylate rubber, whole fluorine rubber and so on. The same kind of rubber because of the different formulations, performance indicators also have a large change. So simply filling in the material bar with nitrile rubber or nitrile-40 is not accurate. For the O-Ring material Chemical Department has special standards, such as: hg/t 2579-1994, hg/t 2021-1991, hg/t 2333-1992, hg/t 3089-2001, HB 5290-1991 and so on. The hg/t 2579-1994 specifically removes the specific category of the material and gives only some performance indicators of the material.