They're the unique elements located in present day synchromesh gearboxes. By trying to keep the main shaft, lay shaft, and clutch shaft at a similar pace, they facilitate easy gear shifting. They don’t have to move over the shaft for your gears to vary. It has an epicyclic equipment arrangement. https://juliuszcbzv.bloggazzo.com/33212876/what-does-automobile-gearbox-mean