I had one years ago, loaned it to someone and never saw it again. It had a trunion for the front legs. In other words, the plank was cut down leaving a round tenon sticking out. The front legs were morticed into a square board about 16" long. In the middle of this board was an oval shaped hole. The tennon went through this hole and had a wedge pin that tightened up in it's own mortice so it didn't press against the other board. Really simple but hard to explain. It was a great design because the front leg "trunion" would self adjust for uneven ground. It gave the stability of 4 legs but always sat flat like 3 legs.