Fredscz, sounds like he has a pretty good method, short of buying a tap. I would like to add to that, if you heat the bolt, it will go in little easier, then just follow the instructions Fredscz gave, and the bolts should not get tight enough to make the blind nuts turn inside the firewall. I use a butter knife to mix epoxy. When it is dry, I use my heat gun to heat the dried epoxy, it crystalizes and scrapes right off. If you have a torch, you might want to heat the bolt with it. Always happy to help if I can. Garry