The gearmotor can also be equipped with optional fourth-stage gear reduction for ratios up to 2,200:1 in the same envelope. This lets companies use a smaller motor without losing torque. The gearmotor works with ac or dc motors, including three-phase and inverter-duty designs. The hollow bore accommodates interchangeable shafts, including stainless-steel shafts. The bore may also be splined, hexed, or designed to handle custom direct-coupled drive shafts. Shielded ball bearings in the motor and output shaft sections handle overhung and thrust loads. Pinion bearings, however, are needle bearings because they withstand the highest radial loads for their size.