4″ X 1″ X 1″ corner brace. Glue or staple.
1″ X 3/4″ X 3/4″ Corner brace – screw on.
3-1/4″ X 1″ X 1″ corner brace
2-3/4″ X 3/4″ X 3/4″ corner brace.
3″ X 1″ X 1″ corner brace