Helix or screw thread; model showing the transformation of the right line generators of a right cylinder into screw threads of various pitch or obliquity

Model of a helix or screw thread which can transform into the right line generators of a cylinder. This is one of a large set of ruled surface models made by Fabre de Lagrange, following designs introduced in the early 19th century. They illustrate surfaces which can be traced out in space by the movement of a straight line,