If you have a Boom unit, the fitting is probably at the end of the unit with a small plastic threaded cap with an O ring. What I did is that I went to the local fire extinguisher shop to find out what kind of fitting they use. They were kind enough to give me a sample of the fitting so I went to a local hydraulic supply shop and purchased a 6 inch piece of pipe and appropriate fittings to connect to the fire alarm
supplier fitting. The other side had to convert from one size thread to the Navtec thread. The thread used by Navtec is the same used in industrial pneumatic tubing used in Air Handling Units control systems. So take the little plastic cap to a local industrial supplier and ask for a pneumatic tubing fitting.