I used a lathe to make an adapter that slides down over the jack piston and then used a large (1"?) drill to make a concave receptacle in the other end to accept the jack point. You could also use a drill press to make this part. I bought a set of the plastic jack points, but they look too soft and flimsy. Buy carraige bolts like m981ms says. You can grind the raised marking off the bolt head to make it smooth. I even use a little grease.
FWIW, I found I need to use some boards to angle the jack base a little under the wing, or the angle between the jack and the wing gets kind of high when the wheel finally lifts off the ground.