Screw thread
![Internal and external threads illustrated using a common nut and bolt. The screw and nut pair can be used to convert torque into linear force. As the screw (or bolt) is rotated, the screw moves along its axis through the fixed nut, or the non-rotating nut moves along the lead-screw.](/Images/godic/202502/16/Internal_and_External_Thread5301.jpg")
![Screw thread, used to convert torque into the linear force in the flood gate.
The operator rotates the two vertical bevel gears that have threaded holes, thereby raising or lowering the two long vertical threaded shafts which are not free to rotate (via bevel gear).](/Images/godic/202502/16/Dubendorf_floodgate5301.jpg")
![Right- and left-handed screw threads](/Images/godic/202502/16/Screw_thread_handedness5301.png")
![The right-hand rule of screw threads.](/Images/godic/202502/16/Right-hand_grip_rule.svg5301.png")
A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread. A screw thread is the essential feature of the screw as a simple machine and also as a fastener.