I have a harbor frieght jack that goes down to 3". It has a 4" flange but still not wide enough for the Xmember. I sometimes use a soft piece of pine wood between the flange and the Xmember because there is more friction then steel on steel and if I am going way up I will slip some 2X6's undre both side of the jack as I go up just in case.
I once had the pumpkin slip off the flange because of carelessness and put a big dent on my gas tank. We all live and learn.