This 3/8" - 1/2" backflow preventer check repair kit, series 008, is used to prevent the reverse flow of polluted water from entering into the potable water supply due to backsiphonage on indoor point-of-use applications. It consists of a check assembly, O-ring, spring, vent O-ring and a bleed screw O-ring and retainer. It is ideal for indoor use on machines or equipment in general plumbing applications.