I'm making a light bulb, and I need to model the "threads" on the metal part of the bulb that let you screw it in to something. I model everything in polygons, but I have no idea how to model a screw shape, rather than just parallel rings on a cylinder.

So I made a bucket shape in NURBS, but I'm totally lost when it comes to trying to get the threads onto it. Can you draw curves onto a 3D surface? Help!