trainsguy

First, I'm not sure if I'm in the right place to post this question, nor am I even sure how to ask this question. I'm a Lionel O gauge guy but I have a question about G scale. Are all flat cars, which are designated as G scale, compatible with each other as far as couplers lining up, connecting and being able to run anywhere within a consist. In a perfect world, I want to be able to find a plain G scale flatcar that will run with any G scale brand, on any G scale track, with any G scale coupler. Is that possible, and if so, what would that flat car be? Any suggestions or information is appreciated because like I said, I don't have the first clue about G scale.