Please forgive my ignorance...

Do our spark plugs have threaded caps on them or are they naked?
During my Tach install, I figured I might as well check the Plug  and good thing I did, it was loose! Before I go to town with my needlenose pliers, I want to make sure that piece I see in the cap is supposed to be there and not the top of the spark plug. Capice?

                                                     Johnny Cat

ps. i hope the tach works when i finally crank 'er up.

Which Tach did you buy and where did you mount it?