These durable speed reducers are used in various industries and especially in the wood industry. They are very rugged and durable.

Legend has it they were designed by the Germans and licensed to the Japanese during WW2 as a tank drive. What ever their original purpose was for, they have proved to be a dependable drive for many modern day applications from conveyors to any number of applications you could think of.

How does it work?   This link is a good article that explains it and even shows diagrams with pictures.