Winterize Sprinkler System Blow Out Adapter: Air Compressor to National Pipe Threads (NPT) Set with Shut Off Valve - Contains all common sizes! Adaptor to winterize underground irrigation sprinkler systems. Includes printed instructions. Includes most common pipe thread combinations! Avoid multiple trips to the hardware stores. Pressure rating: 250 psi with 4:1 safety factor. 100% outdoor rated. Impervious to water and oil. All metal parts are brass. Flexible hose is 3/8" Goodyear Insta-Grip.