Zero backlash, high accuracy harmonic drive gearing that lets engineers pass shafts, wires, tubing or other components directly through the center of the gear, SHF series of hollow shaft speed reducers uses a proprietary S tooth profile to make it both axially shorter and lower in weight than existing competitive products. The speed reducers are also said to provide significantly increased torque capacity when compared with conventional harmonic drive gearing. The harmonic drive can be set directly into equipment, while the housed version has an output flange supported by a large diameter cross roller bearing that reportedly provides exceptional moment stiffness and load capacity. Outer diameter of units in the photo are 104 and 115 mm with a hollow shaft inner diameter of 33 and 29 mm for component set and housed unit, respectively. Gear reduction ratios are from 50:1 through 160:1 in a single stage. Rated output torque is 590 in.-lb. with a momentary peak torque of 2780 in.-lb.