Whether they are shorter or longer depends on the design of a particular car, as the thread is inserted into the beam. Some ...
Lastly, oil on the electrodes or threads is a sign of deeper mechanical problems, but in all cases, you should replace the plug(s). Difficulty will vary greatly depending on the motorcycle.
F connector cables typically carry analog NTSC TV signals, and the plug's socket is easily identified by its threads. Plugs come threaded and unthreaded, both of which fit the threaded socket.