Screw axis
LINE THAT IS SIMULTANEOUSLY THE AXIS OF ROTATION AND THE LINE ALONG WHICH TRANSLATION OF A BODY OCCURS
Screw axes; Helical axis; Instantaneous helical axis; Twist axis; Screw displacement; Screw operation
A screw axis (helical axis or twist axis) is a line that is simultaneously the axis of rotation and the line along which translation of a body occurs. Chasles' theorem shows that each Euclidean displacement in three-dimensional space has a screw axis, and the displacement can be decomposed into a rotation about and a slide along this screw axis.