Single Starts, 2 Starts, 5 Starts, TPI, Lead, HUH?!?

Essentially, lead screws are simply screws that can provide linear motion when a turning motion is applied. Lead is defined as the helix that is common to all screws. A good example of a helix is the DNA molecular structure that exhibits a double helix. In other words, the thread that spirals around the screw. The thread on a standard screw has only one groove that spirals around the shaft that pairs with a nut that reflects the same thread within the inside of the wall of the bore (hole). Different size screws have different leads, or threads per inch. In most cases, even similar sized screws have different threads per inch. Let's say, we have a couple of #10 screws. If the screw has coarse thread, if is considered as having fewer threads per inch than a fine thread screw. A #10 fine screw would have 32 threads per inch, in contrast to a coarse thread having 24 threads per inch.