I've got a NOS Rocket Sprocket hidden in a box somewhere that I've been trying to locate for over a year. I have searched and searched for it, but haven't found it yet. Locojoe is correct. The lever allows the crank to rotate about 90 gegrees and the sprocket is oval shaped and it places the crank in a position to allow more power on each pedal stroke. It also allows the crank to to be placed in the center position for easier cruising. They are neat looking, but a little on the noisey side when pedaling. They were popular in the late 1940's and early 1950's. I'm still looking for mine. Thanks!!!