Adapter plate that mounts directly into a 1-gang box and has holes and cut-ins for mounting the G3-Flex Professional Wall mount. It also has weep holes to let any water that gets in the holes escape.
All screw and nut holes are designed for #6-32. Recommend using 1/2" #6-32 screws or longer with #6-32 nuts for the G3 Professional Mount to the bracket and 3/4" - 1" screws for the plate mount holes.
The grommet hole accommodates 1/4 Inch Diameter Hole Grommets, Inside diameter, 3/8 inch drill hole, 1/2 inch overall diameters. These are the grommets I used: https://www.amazon.com/dp/B000BO9DSA?psc=1&ref=ppx_yo2ov_dt_b_product_details

Model origin

The author remixed this model.

UNIFI G3-Flex Professional Wall Mount 1-Gang Plate