An Acme screw thread is a type of screw featuring trapezoidal threads, a height half their pitch and an included angle of 29 degrees. They are made in several varieties and are often used in industrial applications requiring heavy torque and power transmission such as lathes, milling machines and presses.
Introduced in the later 1800s, Acme screws replaced square-threaded screws, which were difficult to manufacture consistently. Though the frictional component of an Acme screw is high, they engage smoothly with other components when moving, cause less backlash and do not bind as standard-threaded screws do. The trapezoidal shape of Acme screws make them ideal for vertical applications such as lifts when weight must be held without dropping.