[cody]

Yah, that's the issue. The "casting button" (raised bump on the manifold that is thicker than the rest of the pipe) where I tapped the original hole years ago is not wide enough to provide a flat seating surface around the larger hole I had planned to tap for the straight bolt. So by the time I tapped the larger hole, the casting button would be almost gone and I'd probably have to grind it off completely to create a flatish surface for the washer[s] to seal.

Obviously the tapered pipe thread is an effective way to seal or EGT probes wouldn't have been designed to utilize one. I figure I just need to secure a plug that won't melt, and I'm in business.

Thanks ALM I'll call True Value to see if they have a plug made of iron or steel on my break since they're on my way home from work and open in the evening. I'd rather not take another long lunch to go to R&E.