Screw fastening device

An electrical box fitted with at least one screw fastening device to receive a screw for coupling an electrical component to the box, the device comprising:

• a support;
• fastening means attaching said support to a flat surface portion of said electrical box;
• said support including:
• a base having a flat inner surface;
• two spaced side walls coupled to said electrical box and supporting said base with its said flat inner surface in spaced parallel relationship to that flat surface portion of the box, said side walls of the support defining two convergent flat inner wall surfaces disposed in opposed positions in planes normal to said flat inner surface of the base and to said flat surface portion of the electrical box;
• and an end wall extending between said side walls and defining, with said convergent wall surfaces, said base, and said flat surface portion of the electrical box, a rectangular section cavity of truncated triangular shape in plan having an opening between said side walls to receive said screw;
• a pair of generally wedge-shaped screw-engaging members disposed side by side in said cavity for sliding movement between said inner surface of the base and said flat surface portion of the electrical box;
• each screw-engaging member including:
• flat parallel top and bottom faces;
• two opposite side faces, a first one of which extends parallel to the corresponding face of the other screw-engaging member, and the second one of which extends at an inclination with respect to said first face and parallel to the relevant one of said convergent wall surfaces of the support for sliding movement along said surface, the said first face of the screw-engaging member including co-operating recesses having internal grooves in which together define a thread complimentary to that of a screw to be received in said screw fastening device;
• and,
• spring means extending between said end wall of the support and said screw-engaging members and biassing said members in the direction of convergence of said convergent wall surfaces of the support so as to maintain said first faces of the members in co-operating relationship and said second face in sliding contrast with said convergent wall surfaces;
• whereby said screw can be inserted between said screw-engaging members, causing alternate relative movement of the members along said convergent wall surfaces of the support in directions against the biassing effect of the spring means and back to their normal positions under the action of said spring means as the thread on the screw rides over the corresponding thread defined by said recesses, the screw being held in its inserted position by said screw-engaging members and the thread defined by said recesses allowing the screw to be axially displaced by rotation in the appropriate direction.