Here's a couple of pictures. If you look closely at the first one you will see th threaded pipe is tapered. So it fits in the tube about half way before the threads engage. The theory is you just srew it in and then pull it out and the tube comes out easily. The transom sometimes does not expand enough sometimes or starts to break under the stress. if I recall correcly, the pipe is standard 3/4" fittings.
T-Section
T-Section in Spark Plug Tube
