GO to any auto parts store and look at the threads on the three valve motor's plugs. They're "rolled" on the edges of the threads. They don't come to a point like regular plug threads. Almost like the threads are incomplete. It's a wonder they even tighten up.
Actually, a rolled thread is much stronger than a machined thread. So there is some other problem with those plugs. The 2-piece design is the biggest problem.
