I'm sure if you go to the Loctite website, it will tell you what each type is good for. I've used the 242 (blue) on muffler nuts and bolts, the green on smaller hardware (#2), but I've only used the red on things I don't want to take apart again! Follow their directions, they are worth reading. Loctite holds up to muffler temps very well, but keep it away from plastic.