LANTERN

In watchmaking, the term lantern first refers to a small holding tool: the Screw Lantern (or Lantern with Screws) is a metal cylinder pierced around its circumference with staggered-diameter holes, designed to hold a Screw by its head while one Files or adjusts the Length of its shank before redoing its Threading. Lanterns of similar design also serve to hold small components — rods, arbors — during their turning or finishing. By analogy of shape with the lighting object, the word also refers to the Lantern pinion (or trundle pinion), an ancient form of pinion made up of two circular plates connected by several parallel cylindrical rods, the trundles, which act as teeth when meshing with a wheel. Sturdy, little sensitive to wear, and easy to manufacture, this type of pinion long equipped tower clockwork (bell towers, public clocks) and certain roughly made movements, before being largely supplanted by the cut leaf pinion, with better efficiency and more regular friction.