At any point along the length of the threaded portion of a screw the thread is going to "be at a certain angle". Does this make sense? Obviously, this is fairly complicated.
What we're doing is defining an object - here in quite literally the physical sense. In our model, which is a collection of words, we would define assorted objects. Let's say we were describing, oh, a camera. It would have various components, and each would be an object. Well, for each object, we would ... in a way, don't have to do this ... if we list a portion of the model as describing some object, implicitly, a coordinate system is created. We could say, then, that the tip of the screw is the origin, and the length of it extends along the z axis in a positive direction.
I'm fantasizing being able to print out very small screws. Let's say the diameter of the screw is 2 millimeters, and the pitch of the threads is 1/4 millimeter per rotation. We could originate the rotation on the y axis, in the positive direction, rotating from there towards the y axis positive direction.
