Gates uses 3 lobe fitting for Shimano Alfine hubs. The earlier version cogs just slid on and off the hub & would flex slightly. This risked creating a drag on the drivetrain. The new 3 lobes help keep the cog in a stable position. This reduces drag, however it is more difficult putting the cog on and off. Be careful installing the cog, a simple scratch during install may cause a long term failure of the cog.