I wanted to keep my printer stable and leveled and didn't find anything out there so I made this. I used some o-rings I already had (Ideally one would use domed rubber footings). I used a robust 20mm-4 trapezoidal thread. Works well for me.
3D printers aren't perfect so you're actually getting threads with tiny steps, so when assembling, screw in the foot into the bracket 1/4 to 1/2 turn at a time then back off some and screw in another 1/4 to 1/2 turn until you're all the way through (Like tapping). You don't want to seize the parts together. The screw should go in and out smoothly after that.
I've included the solidworks 2013 files ( steps too ) if you'd like to modify it for your needs.