This is an experimental plate that is compatible with the ConnectIt mounting system. Note that anything you print with plastic will be notably weaker than an actual ConnectIt plate. Something like this may work well for mounting much lighter things to the bracket.

There are 4mm diameter holes for both VESA 75 and VESA 100 (75mm square and 100mm square) The large square is 120mm on each side and 2mm thick.

I'd recommend printing this with extra perimeters and high infill. For example, I did mine with 5 perimeters and 80% infill.