The thread is a profiled indentation that runs along a helical line wound around a cylinder. The type of lead screw is defined by the profile shape, the pitch, the number of threads and the direction of rotation. You will find more terms related to lead screws in another blog post. Basically, lead screw drives are machine elements that convert rotary movement into linear motion. In this blog post we look at one of the common thread sizes: the 10×3 thread size.