Hello everyone, I am trying to design a self reversing screw. What I am doing is, I am sketching a rectangle and using extruded cut option in Solidworks, cut it along a helical curve. One more and this time in the opposite direction. It comes out nicely. Now what I don't know is, should I use a rectangle or a trapezoid for the profile? I examined a self reversing screw and I am sure it was a rectangle. Though I've found a video on youtube and the guy there uses a trapezoid. Does anyone know this? Trapezoidal thread seems more logical but then I wonder why the one I've seen is rectangle. I'd like to get as much information as possible about self reversing screws, especially the relationships between the screw dimensions and the small part that is going around (sorry I don't know its name). Google doesn't help much. Here is the video: (Skip to sixth minute) Thank you.