I just got back from Unlimited Oxygen in Indiana. Jack and David were great! I bought 2 M-20s and they upgraded my M-10 to an M-20. We chained two M-20s for the outer flame and my upgraded M-10, now also an M-20, connected to the center flame. The end result? I have this beautiful flame! Ricky, my hubby, no longer has to drag oxygen tanks up and down the stairs and I can actually use my outer flame all the time if I want!