A connection system for joining rectangular wall frames fabricated from pairs of rectangular cross section tubular side frame members and rectangular cross section tubular top and bottom frame members utilizes identical connectors, such as a single size machine screw and identical threaded inserts to provide upper and lower interconnections. Three different interconnections can be made using the single size machine screw and insert, the latter inserted into the open upper ends of the rectangular cross section tubular side frame members. Frame closure panels can be attached in a simple and secure manner.