Ford Repair: E3 spark plugs..., e3 spark plugs, autolite plugs

Question
I have a 98' 3.0 L Ford Ranger. My simple problem has evolved into a significant one. I put a set of E3 plugs in some time ago and soon had a problem where the motor started running hot and poorly. Upon inspection I found one of the plugs electode burned away??? A mechanic said engine problems as the motor has many miles ect...I decided the new plugs are just too hot for an older motor and wanted to reinstall the OEM Autolite plugs. Now the problem begins...I can't get the new plugs to thread into the block!! I can't even get them to start to thread. I suspect that the E3's have changed the threading because I can easily reinstall the E3's but can't even start the Autolite's. This is insane. I have changed the plugs on this vehicle 10-12 times easily over the course of 9 years that I've owned this truck. Am I crazy? Is it possible that these suspect plugs have cut a new start thread that now only matches the E3 plug? and what can I do to resolve this? I am at a loss and very pissed about what I think has happened.

Answer
Ok, this is an easy one. Goto your local parts store, during 9-5 workdays. Ask for their parts pro. But first you should know that autolite is a substitute, not OEM. Motorcraft, is the OEM. Try matching the thread size and count on the E# and the motorcraft.