I found that all of the other thumb screws that were offered were difficult to print, because they all had overhangs. This design is simple to print (with no overhangs) and very simple to use.
Print 3 of the thumb screws and then thread them onto the screws on the underside of your Solidoodle printer. You may want to use some acetone or Duco Cement on the threads. If the thumb screws do not "grab", you can use a little super glue. Do not thread the thumb screws on too far: leave yourself enough room for adjustment. The thumb screws are especially useful if you are printing with a glass plate over the original bed.
Some people had problems with the printer bottoming out because the knobs were too tall, so I now provide a version without the "cone".