Later in 1929, Simplex’s initial single pulley wheel design (see French Patent # 669,030) appears to acquire the option of a second pulley wheel - but this is rigidly fixed in relation to the mounting bracket. The chain is tensioned by movement of the whole gizmo.

• Publisher: L’Institut national de la propriété industrielle
• Inventor: Lucien Juy
• Country: France
• Date: French application July 1929
• Derailleur brands: Simplex
• Derailleurs: Le Simplex