Hello So at the moment, I am reading through Shigley's Mechanical Engineering Design book. I've come, at, last, to the first application chapter. Screws, Fastners.. etc. Since I lack experience, what I am trying right now is to visualize every single diagram in this chapter and move through equations slowly. Attached to this post is an image. It is written in the book as follows 'First, imagine that a single thread of the screw is unrolled for exactly a single turn. One edge of the thread will form the hypotenuse o a right triangle whose base is the circumference of the mean-thread diameter and whose height is the lead' To be honest, I've tried hard visualizing this and searched all over the web, but I have no clue. I can't imagine it. Can someone give me a hand over here?? I think if we unwrap one turn the hypotenuse would be the circumference??... Moreover, in the attached picture, what is F (the load we want to push up or down)?? and why is the nut stationary and is it stuck to the bolt.. Why is there F/2 on the each side if we only have ONE nut?? I will be very interactive in this post because I had very hard time to understand it and look through the internet. Thanks A LOT to whoever contributes with an answer no matter how small. Thanks in advance and sorry for the long post. MERRY CHRISTMAS!