I had a fuel pressure vacuum gauge (harbor freight) but was not able to get it hooked up to the test port (shrader valve). I was going to get an aftermarket adapter or buy a gauge from kennedy, but did not want to drop the coin. With this adapter I can test fuel pressure at each fuel filter head. I have a secondary filter and wanted to isolate the primary. I am getting the typical 2-3" Hg with a fresh filter and 6+ after using (after a top end clean). It is somewhat of a pain to have to connect this thing up to test, but I don't do it that often. I may use this in a more permanent setup and just run hoses through the firewall to monitor.