Brass Push>Connect Air Brake Tube Fitting, 0.50 Inch Tube OD To 3/8-18 Male NPT, Straight

150 psi is actually the top of its rated range, so you're right at the limit rather than comfortably below it. For air brake applications running at typical system pressures, that ceiling is generally sufficient. The fitting also handles vacuum on the low end, so it covers the full spread of what most air brake circuits see. Just make sure your tube is cut square before insertion and seated all the way in before you put it under pressure.

It is set up for 0.50 inch tube OD on the push to connect side and 3/8-18 male NPT on the threaded side, straight configuration.

This fitting is designed specifically for air brake systems and meets D.O.T. FMVSS 571.106 and SAE J1131 standards, so it should be a good fit for your application. It's made from CA360 brass for durability, and the EP O-ring will give you a reliable seal.