A fuel additive bottle has a neck and thread pattern that allows insertion into a capless fuel system so the bottle's contents can be poured by gravity into a fuel tank. The neck of the bottle is elongated and has a diameter of approximately 0.854″, and the novel thread pattern includes thread interruptions that form at least one threadless path. In use, the spring loaded tabs of a capless fuel system are depressed by the threadless path portion of bottle, thereby triggering the self-sealing mechanism to open, so the fluid receiving aperture is exposed. The use of the threadless paths facilitates the safe and easy entry and removal of the bottle from the capless fuel system.