A structural frame assembly is provided that includes mechanically interlocking components. The frame assembly has rails that interconnect with each other at joints that include brackets that engage the rails and nuts that are held in cavities of the rails that are connected to slots that extend through outer surfaces of the rails. Bolts may extend angularly through bores of the bracket and the slots of the rails to operatively engage a nut being held in the cavity. Tightening the bolts may draw the nut angularly through the cavity in a manner that automatically self-aligns the brackets and rails to establish precise joints.