Abstract: A ready-to-assemble furniture (“RTA”) system in which a seat, such as a sofa, comprises a seat base with a seating portion having a pair of preattached arm rests on opposing sides of the seating portion, and a separate backrest. The sofa has a transport configuration where the backrest nests on the base between the arm rests and is convertible to a use configuration by a simple upward lifting of the backrest, a partial rotation of the backrest of about 90° , lowering of the backrest onto elongate polymer KD brackets having a rearward inclination on the arm rests until a pair of slots of the backrest panelar side members is seated on the KD brackets. Each KD bracket having a wedge portion at the arm rest surface and a flange portion displaced from the arm rest. The seat may be boxed with instructions for assembly attached to the sofa.