Flat pack (ready-to-assemble, knockdown) furniture has become the most extensive furniture model produced with the development of wood-based board materials technology. It is especially preferred in the building industry as a model suitable for mass production. In this study, the resistances of dowels and screws, which are used in a widespread manner as joining material at the corners of ready-to-assemble furniture, were investigated against tensile and compression resistances in the diagonal direction. Chipboard (CB), medium-density fiberboard, and gaboon mahogany plywood (GMP), 14, 16, and 18 mm thick, were used in this study. Dowel + screw, screw, screw + polyvinyl acetate (PVAc) adhesive, and screw + polyurethane (PUR) adhesive joining were implemented for the L-type corner models obtained from wood-based board materials. According to the results obtained, the highest moment-carrying capacity values in the L-type corner joining were provided in the 18-mm GMP board joined with screw + PVAc adhesive and screw + PUR adhesive for both tests. The joining made without adhesive and the CB materials produced the lowest moment-carrying capacity values.