Bed foundation beams are sandwiched by a compression bar extending parallel to the first and second rails and moved towards the first and second rails while being conveyed. Further, the first and second rails and the spacers are sandwiched against spaced fixtures on an endless chain. While being compressed and sandwiched, staple guns fasten the rails and spacers together. The fixtures include front and back stops, with the back stop pivotable about a fixture axis to be movable by a cam moving in a cam track from a pushing position extending perpendicular to the endless chain and abutting with a trailing edge of one of the spacers and a non-intervening position after the staple gun and before the sprocket of the endless chain to reduce the apparatus footprint.