Reinforcing plate (fishplate)
2-1/2" x 5", used to reinforce a butt-welded joint. 10 ga mild steel. Available with or without a hole in the middle.
The plate can be put on the inside or outside of the frame or holes can be drilled in the frame and rosette welds can be used to weld the plate inside the frame tube.
Available solid or with a 1-1/2″ dia. hole.