Changing single gauge regulator to dual

A single gauge regulator came with my kegerator. I bought the correct gauge and was wondering if I can take the bolt/plug out of the regulator and install the second gauge. If yes, what can I expect when I remove the bolt? Will there be a washer there? Will I need a washer?

Honestly, there's no need for a dual gauge. I have a dual gauge, and the only thing it does is tell me how much pressure is in the co2 tank. It's worthless though because it doesn't read a pressure drop until the tank is empty. I'm not sure if other people's gauges work this way...but my second gauge has never been of any use to me. All you really need to know is serving and carbonating psi. If you have that, don't worry about extra stuff.

Remove bolt, install gauge. No washer, use teflon tape. You're done.

Take a close look at the threads, because some regulators use left-handed threads on the high-pressure side.