second diagonal member 4 a the second diagonal member 4 a and first diagonal member 4 b are adjustably joined by a joint 7 the joint 7 is adjustable and thus allows an installation mechanic to increase tension on the diagonal members 4 a 4 b after the wall panel has been installed an example of an adjustable joint is shown in fig3 the joint may be readily made from two pieces of conventional c channel steel 7 a 7 b connected by at least one bolt 7 c the exemplary joint illustrated in fig3 uses four bolts 7 c and appurtenant washers and nuts one may use more or less bolts as appropriate it may be least expensive to fabricate and install this kind of joint using only one bolt sited at or near the center of the face of the c channel the steel c channel 7 a 7 b may be reinforced with a block 7 d to prevent the bolts from pulling through the face of the c channel the steel c channel may alternatively or in addition be reinforced with a flange 7 e to maintain the c channel in its proper intended conformation one may as illustrated use a nut to anchor the bolt 7 c alternatively one may thread a hole s in the reinforcing block 7 d and screw the bolt directly into the block eliminating the need for a nut similarly if the c channel stock has appropriate strength one may thread a hole in the.