Johnny Chung Lee published a great design for a $14 Steadicam (http://littlegreatideas.com/stabilizer/diy/). However, the camera attachment relies on a wing nut and a washer, so when the camera is not attached, the washer is loose, and you have to flip the wing nut to hold it in place.
I figured I could make a plastic knob that fits around a nut, and fills the role of both the wing nut and the washer, thus keeping things simpler.
I decided to try out OpenSCAD to do this, and it turned out to be perfect. It's so easy to change things that I have included a file for a 1/4 inch screw, which fits most cameras, and another version for a 3/8 inch screw, which allows attaching alternative tripod heads.
This is a generally useful piece for attaching cameras to all sorts of home-made camera mounts.
Print out the size that you want (1/4 inch or 3/8 inch), and pop an appropriate-size nut in the opening. I find it works well to put the nut in before the piece has cooled down, then as it shrinks it is held in place really firmly. Of course, you can just glue it in place.
I also find it useful to attach a neoprene washer to the top of the thing, to provide even pressure to the camera base.
To use it, loosen the knob, ie. turn it so that it goes away from the end of the bolt. Thread the camera on to the bolt, and point it in the direction you want. Tighten the knob against the base of the camera to hold it in place.