This 1941 patent shows a Lewis single pulley model. The derailleur is a classy item for the time, with the main arm manufactured using a complex casting (rather than a flat plate) and the pulley cage sporting a curvaceous profile.

• Publisher: L’Institut national de la propriété industrielle
• Inventor: Louis Villemus
• Country: France
• Date: Priority date December 1941
• Derailleur brands: Lewis
• Derailleurs: Le Lewis?