Hey I was cleaning up this old Clinton model 404 the other day getting it ready to finish it up. (It starts on starter fluid now. Just trying to find the best carb out of the pile to use on it.) But I never noticed the circled thing before. The way it's set into the engine makes it seems as though the cam shaft turns it from below. There is a set screw in top too. Is this something I could put a shaft into and have a reverse gear? Anyone know what this is used for? Oh and its threaded. Thanks.