The Standard Repair Kit is compatible with the 2-1/2”-4” Model 350A, 375, and 475, and the 4” Model 350 and 450 Backflow Preventer. Repair Kit components conveniently include two Check O-Rings, eight Poppet Bolt O-Rings, and two Seal Rings. Repair Kits are sold as accessories for quick and simple repair needs, providing long-lasting protection from both backsiphonage and backpressure of polluted water into the potable water supply.