Frame construction for box spring assemblies

A generally rectangular frame for supporting the springs in a box spring assembly consisting of horizontal side and end rails, a plurality of transversely spaced cross rails supported on and extending between the side rails, and a center rail supported on and extending between the end rails and interlocked with the mid portions of the cross rails so as to support the cross rails intermediate their ends. The cross rails and the center rail are longitudinally arched to provide a mattress foundation which is convexly arched in two directions when viewed from above. Telescoping bracket supports are provided for mounting the ends of the center rail on the wood end rails so as to eliminate the necessity for slotting the end rails and uniquely shaped tabs are struck out of the cross rails to enable easy interlocking of the center rail with the cross rails during assembly of the frame. The cross rails are shaped so that they have narrow strips of metal at their ends to enable use of a conventional stapling tool for attaching the cross rail ends to the wood side rails.