Abstract: Adjoining edges of sheets of pre-coated metal or other rigid material may be interlocked against movement transversely apart by forming the edge of a first sheet with a lock member constituted by a transversely offset reverse flange having at its extremity an outwardly directed first hook member and forming the adjoining edge of the second sheet with a transversely offset projecting flange whose extremity forms a second hook member directed inwardly. The sheets may be locked together by superposing the second hook member over the first hook member with the projecting flange behind the reverse flange and with orthogonal flanges spaced slightly apart and relatively rotating the sheets to a fully interlocked position defined by abutment between the orthogonal flanges. The above arrangement can advantageously be used in the vertical rear corner joints of a pre-coated steel cabinet where it is helpful to be able to assemble the cabinet from its major components without the need for pop-riveting or the like.