Why did I get this male to male brass piece with my Comet Static Pressure Washer Package? I don't see where to use it.

That brass adapter with the tape on it is something we send with our Original Mosmatic/MTM sprayers, along with the stainless 3/8” coupler to connect to a pressure washer hose.

We also sent a 1/4” BSPM to 3/8” NPT adapter that replaces that brass piece for the Comet systems. We send the brass piece anyway since it comes with the kit, but you don’t need it. Connect the 1/4” to 3/8” adapter to your hose and the stainless coupler, then plug your gun in, and you’re good to go.