Parker Back Up Ring Seal 180004N0300 prevents migration of O-rings into the sealing gap when subjected to high pressures. Parker Parbak Back Up Ring is a Parker Parbak standard rubber back-up ring of contoured design. It is intended for use in dynamic and static seal applications. Features of Parker Parbak Back Up Ring: Elastic memory permits Parker Parbak Back Up Ring to be stretched into place for assembly without preconditioning or cutting. Continuous construction prevents damage to the o-ring seal. Lubrication is enhanced by rubber which absorbs system fluid and does not plate out on rubbing surfaces. We have in total 4 kinds of brands back up ring with a total number of 440 types of back up rings. 1, Parker back up ring 2, HITACHI back up ring 3,Sidahang back up ring 4,Hallite back up ring