This patent covers the extensive shaping of the inner pulley cage plate of Simplex's 'T' type derailleurs. The shaping in question was designed to prevent the derailleur getting all-caught-up in the spokes of the rear wheel. In 1973 this was impressively innovative and advanced. Derailleurs had long had some defences against getting trapped by spokes, but this patent took the concept to a whole new level. It was not until the early 1980s that Shimano did something similar.