The boat we purchased in June had the gas cap stolen just before we bought it....the one we were given with it wouldn't thread more than a quarter of the way.
Got on Amazon and bought a Moeller Replacement Cap/filler neck just to be done with it and know we had something that was right. It was only about $26 for the entire piece. Well worth it in my opinion for piece of mind. Came with a gas key, screws, and gasket to mount filler neck to boat.