Granville Lock Thread? I'm guessing the metal epoxy I I just bunged in there will be stronger than thread lock anyway? If I knew someone who had a little welder Id weld the thing together. It's a stupid design really, the mirror catches the wind which twists the arm anticlockwise, so the pressure of the wind against it is naturally wanting to unscrew it, combined with bumps and vibration etc. Anyway, well see if this works. The mirrors on this bike are my nemesis.