Hello There! I wanted to install a different rear view mirror on my Astra H, and after looking over the available options ( ie factory ones ) I came to the conclusion that I would prefer to adapt and mount a VW frameless & self-dimming rear view mirror ( part number 3G0857511AD9B9 ). Connecting the mirror to the car so that it can self-dim is simple, you would need to supply 12v power to it and it does the rest itself ( + to pin 1 , - to pin 2 on the mirror connector ) Now the design is made so that the mirror can be mounted to the exciting mount glued to the windshield. Initially, I made this design to be friction fit, but after about 3 or so months of use the fit started to loosen and the mirror would start sliding off. So as a simple solution, I made a 1mm hole where a straightened-out piece of a paper clip could be inserted to act as a pin holder/release.

Parts needed for installation:
4 x 10mm m3 screws
4 x 20mm m3 screws
1 paper clip or something of a similar diameter ( less than 1mm )