A transmission assembly for use in a hand-held surgical instrument, the transmission assembly comprising: a housing; a main drive motor supporting a main drive gear; first and second output gears (120, 122) operably coupled to the main drive gear and configured to rotate in response to a rotation of the main drive gear; first and second output shafts (106, 108) rotatably supported in the housing; and a selector cam associated with the first and second output shafts, wherein the selector cam is configured to move between a first position, in which the selector cam non-rotatably couples the first output shaft to the first output gear and the second output gear is rotatable relative to the second output shaft, and a second position, in which the selector cam non-rotatably couples the second output shaft to the second output gear and the first output gear is rotatable relative to the first output shaft, further comprising: a first coupling shaft non-rotatably coupled to the first output shaft, wherein the first coupling shaft is configured to non-rotatably engage the first output gear when the selector cam is in the first position such that only the first output shaft of the first and second output shafts rotates in response to the rotation of the main drive gear; and a second coupling shaft non-rotatably coupled to the second output shaft, wherein the second coupling shaft is configured to non-rotatably engage the second output gear when the selector cam is in the second position such that only the second output shaft of the first and second output shafts rotates in response to the rotation of the main drive gear, wherein each of the coupling shafts (130, 132) has a tab or protrusion that extends through a slit defined in each of the output shafts such that the first and second output shafts (106, 108) rotate with and by a rotation of the respective first and second coupling shafts (130, 132); and characterised in that the transmission assembly further includes a bracket disposed about each of the output shafts (106, 108) and fixed within the housing, the bracket defining a plurality of apertures configured for receipt of the tab of the respective coupling shaft when the coupling shaft is in a distal position. a housing; a main drive motor supporting a main drive gear; first and second output gears (120, 122) operably coupled to the main drive gear and configured to rotate in response to a rotation of the main drive gear; first and second output shafts (106, 108) rotatably supported in the housing; and a selector cam associated with the first and second output shafts, wherein the selector cam is configured to move between a first position, in which the selector cam non-rotatably couples the first output shaft to the first output gear and the second output gear is rotatable relative to the second output shaft, and a second position, in which the selector cam non-rotatably couples the second output shaft to the second output gear and the first output gear is rotatable relative to the first output shaft, further comprising: a first coupling shaft non-rotatably coupled to the first output shaft, wherein the first coupling shaft is configured to non-rotatably engage the first output gear when the selector cam is in the first position such that only the first output shaft of the first and second output shafts rotates in response to the rotation of the main drive gear; and a second coupling shaft non-rotatably coupled to the second output shaft, wherein the second coupling shaft is configured to non-rotatably engage the second output gear when the selector cam is in the second position such that only the second output shaft of the first and second output shafts rotates in response to the rotation of the main drive gear, wherein each of the coupling shafts (130, 132) has a tab or protrusion that extends through a slit defined in each of the output shafts such that the first and second output shafts (106, 108) rotate with and by a rotation of the respective first and second coupling shafts (130, 132); and characterised in that the transmission assembly further includes a bracket disposed about each of the output shafts (106, 108) and fixed within the housing, the bracket defining a plurality of apertures configured for receipt of the tab of the respective coupling shaft when the coupling shaft is in a distal position. a first coupling shaft non-rotatably coupled to the first output shaft, wherein the first coupling shaft is configured to non-rotatably engage the first output gear when the selector cam is in the first position such that only the first output shaft of the first and second output shafts rotates in response to the rotation of the main drive gear; and a second coupling shaft non-rotatably coupled to the second output shaft, wherein the second coupling shaft is configured to non-rotatably engage the second output gear when the selector cam is in the second position such that only the second output shaft of the first and second output shafts rotates in response to the rotation of the main drive gear, wherein each of the coupling shafts (130, 132) has a tab or protrusion that extends through a slit defined in each of the output shafts such that the first and second output shafts (106, 108) rotate with and by a rotation of the respective first and second coupling shafts (130, 132); and characterised in that the transmission assembly further includes a bracket disposed about each of the output shafts (106, 108) and fixed within the housing, the bracket defining a plurality of apertures configured for receipt of the tab of the respective coupling shaft when the coupling shaft is in a distal position.