A frame member is provided for a structure. The frame member includes a generally flat, elongated first surface having an elongated slot therein extending along an axis. The slot is defined by first and second converging sidewalls lying in corresponding planes which are at acute angles to the first surface. A first diverging outer abutment wall is generally perpendicular to the first converging sidewall and a second diverging outer abutment wall is generally perpendicular to the second converging sidewall. A first diverging inner abutment wall is generally perpendicular to the second converging sidewall and a second diverging inner abutment wall is generally perpendicular to the first converging sidewall.