The Osgear Grand Sport is a child of many parents. Osgear is the brand of the London-based Constrictor Tyre Company and is engraved on the mounting plate, Super Champion is the brand of Paris-based Oscar Egg and is stamped on the main arm, and finally, in small print on the back of the mounting plate, it is revealed that the design is licensed from Cyclo.
The derailleur itself is a classic, chainstay mounting, pull-chain, touring design. It was first released as a Super Champion Grand Sport in 1938, and continued in production in various guises until at least the mid-1950’s.
Chain tension was provided by a spring attached at one end to a clip on the chainstay behind the bottom bracket, and at the other end to the bolt close to the guide pulley.