Tru-Flate Steel Air Line Coupler Plugs feature unique, high-performance design features and durable materials that work better and last longer, providing 100% reliability. Heat treated, cast and machined, plated steel construction offers high strength, durability, and corrosion resistance. Rated at up to 300 PSI. Tru-Flate is part of the Plews & Edelman group. Plews Manufacturing and Sales Corporation was originally founded by R. G. Plews in 1927. At that time, the railroad industry was the primary focus for the company's extensive line of oil cans. As the transportation industry went from trains to passenger cars and trucks, Plews shifted their focus to developing the tools necessary to service this new mode of transportation. Fast forward 90 years and Plews has become part of Plews & Edelman. Today, Plews & Edelman is a leading designer, manufacturer and distributor of a broad range of automotive parts and tools sold to the vast majority of mass merchant, retail auto parts stores and wholesale automotive parts and industrial distribution outlets, worldwide.