HMHG-Ⅰ Series Unit (Hollow Shaft) Harmonic Gearing HMHG-I series flexspline belongs to the hollow flanging standard structure and there is a large-caliber hollow shaft hole in the middle of the wave generator cam. Support bearing is also designed inside the power drive gearbox. The high quality harmonic reducer is fully sealed and easy to install, and especially suitable for the situation where there is a need to thread through the reducer center.