A German-made 14 speed all-internal gear hub for bikes. Most bike hubs use cogs. In theory you take a bit of an efficiency hit by using gears instead of cogs, but it turns that most bike’s chains are not properly maintained nor in perfect alignment – which lowers their efficiency in practice. Thus the all-internal hub which always has perfect chain alignment and only requires a 1 oz. oil change per year in maintenance ends up being more efficient. You can also shift the full rage of gears while standing still or with pressure on the pedals. You also avoid the usual derailment, fragility, and chainsuck issues of a normal transmission (this is why many professional downhill riders are switching to them). It weighs a bit more than all the components it replaces in a traditional bike tranny but gives the bike an overall cleaner look. Also, since normal bike gears overlap their range this hub’s 14 speeds is equivalent to 27 or more speeds of the traditional derailleur tranny. I have been riding mine now for a while and would never go back.