The key diameter refers back to the widest diameter of your thread. For the screw shaft, it really is the gap amongst two opposing crests, when to the nut, it is the gap concerning two opposing roots. Countersunk screw heads attribute an angular form underneath the head from the screw. https://rowansckry.blogmazing.com/28893941/lead-screw-examples-things-to-know-before-you-buy