screw

A screw is a shaft with some type of helical groove or thread formed on its surface. The threads usually engage with mating threads on the inside of a hole in some type of appliance that the screw runs through, such as a nut. When the shaft of the screw is turned relative to the stationary threads, the screw moves along its axis. It is one of the six classical simple machines. A screw can convert a rotational force (torque) to a linear force and vice versa. The screw's pitch, the separation between adjacent threads, determines the mechanical advantage of the machine. More threading increases the mechanical advantage. A rough comparison of mechanical advantage can be done by dividing the circumference of the shaft by the distance between the threads