The flat head bolts belong on the inside of the top ring. This means the cap nuts are on the outside of the top ring.
The holes in the legs for the top ring are within two inches from one end of the square legs. Push the bolt from the inside of the ring through the ring holes and the square leg hole. The leg fastens on the outside of tank and the nut outside of the leg.
The tank will not fit into the stand if you do not use the flat head bolts on the top ring. The wedgies or triangle pieces hold the conical part of the tank and keep it from sliding down or wobbling. The narrow end of the wedgie points toward the top ring and fits inside of the leg to the leg holes a few inches below the top ring.
The stand has four legs and is very stable.