On my old MTD blower one drives the wheels and one drives the auger, that's why trying to install a single shaft replacement is a pain, how ever there are some full write ups on doing it over on one of the snow blower forums, but way out of my league.Mine's a single, already off of the machine at my local small engine shop. I'm thinking it was on a simple snow thrower with forward only....usually the reverse models have the dual shaft.