Corner Bracket with a footprint of 35mm x 30mm. Screw holes support screws with a diameter of 3.5mm or less. You can, of course, scale the model up or down to perfectly fit your screws.

Printing with increased infill and a higher number of walls as well as a stronger material such as PETG or ASA yields a strong and capable part. They worked wonderfully in helping me build a small winter enclosure for my outdoor plants!