When you screw in a normal bolt i've heard it spreads the coils slightly, which is what helps keep it in. You don't need any loctite, they're not likely to come out. Regarding the length of the insert, I just screwed mine in so it was about 1/2 threads below the top of the mount, then left it in. Are you sure that you're talking about the length when you see M5x0.8 and M5x1.0? That last number is the thread pitch, not the length of the coil.