Turns out the top half of this hole is untreaded, and the bottom hal is threaded.
For those that live in areas that dont do SMOG Testing you can get a M18 x 3.25" Metric bolt, and use some red thread locker on the first 1/2" of threading. If its nearly impossible for you to find a M18 bolt, and you dont care about your manifold I have a solution. Get at 5/8" x 3.25" SAE Hex Bolt, and use red tread locker on the first 1/2" of threading. Get a good size 1/2" driver wrench and torque it down til you feel like yours going to break your hand.
Viola! Problem solved and the tread locker will keep it in there for a long time. The bolt does look funky though since its a shinny peice of metal standing out of your manifold. Kinda looks like a hood ornimant for your engine.
But hey now my exhaust is Lexus Quiet...