The 2100 is light duty with 3/4 axle and the 2200 has 1 inch and is heavier duty. I don't even see the 2100 on the manufacturer's product list. Discontinued? http://www.hydro-gear.com/residential/
i noticed that as well...but its still being installed on the quest?...now i'm not sure i want to go with either of them and bump to a 2800 transmission for longevity
https://www.exmark.com/products/mowers/zero-turn/quest/quest-e-series?m=QZE708GEM42200