The brackets are used to clamp mitered joints like picture frames and boxes. The miter angle does not need to be 45 degrees. When 3D printing use 50% or more infill for strength. Glue 80 or 100 grit sandpaper to the flat inside surface to prevent the bracket from slipping during use. The pictures show how the clamp brackets are used.

More woodworking gadgets: https://www.instructables.com/3D-Printed-Gadgets-for-Woodworking/ https://www.instructables.com/More-3D-Printed-Gadgets-for-Woodworking/