Although there are several designs shown on this patent, the key mechanism is the one shown in the picture above - featuring a cable, rigidly clamped to the derailleur body, but running over a moving roller in domed cover. This was the signature Westminster derailleur, and they were popular enough to ensure that, even today, you still come across them fairly frequently.

• Publisher: L’Institut national de la propriété industrielle
• Inventor: Jean Lionard and Jean-Pierre Champin
• Country: France
• Date: French application July 1935
• Derailleur brands: Lionaxe
• Derailleurs: Lionaxe Westminster Route