A gear box includes an output shaft defining multiple output drivers and includes a plurality of gear sets having the same diametral pitch. A common input shaft is operatively attached to each of the plurality of gear sets such that the gear sets rotate continuously and concurrently with rotation of the input shaft. Each of the output drivers is operatively attached to the output shaft and rotatably driven by a respective one of the plurality of gear sets. The multiple output drivers share a common axis of rotation with the output shaft. The output speed of the gear box may be changed by disconnecting one of the output drivers from a driven device and reconnecting another one of the output drivers to the driven device. The output speed of the gear box may be changed without having to disengage and/or change out any of the gears in the gear box.