A shaft assembly for selectively interconnecting an end effector and an electromechanical power source, the shaft assembly comprising: an outer tube; a rotatable drive shaft supported therein; a proximal neck housing supported at a distal end of the outer tube; a distal neck housing pivotally connected to the proximal neck housing, wherein a distal end of the distal neck housing is configured and adapted for operative connection with the end effector; a pivot pin interconnecting the proximal neck housing and the distal neck housing; and a gear train supported in the proximal neck housing, on the pivot pin, and in the distal neck housing, wherein the gear train includes: a proximal gear rotatably supported in the proximal neck housing and being coupled to a distal end of the rotatable drive shaft; an intermediate gear rotatably supported on the pivot pin and being in operative engagement with the proximal gear; a distal gear rotatably supported in the distal neck housing and being in operative engagement with the intermediate gear; and characterised by a pair of output gears (239a, 239b) rotatably supported in the distal neck housing and each being in operative engagement with the distal gear, wherein each output gear defines a coupling socket (239a 1, 239b 1) each configured to selectively receive the drive axle of the end effector. an outer tube; a rotatable drive shaft supported therein; a proximal neck housing supported at a distal end of the outer tube; a distal neck housing pivotally connected to the proximal neck housing, wherein a distal end of the distal neck housing is configured and adapted for operative connection with the end effector; a pivot pin interconnecting the proximal neck housing and the distal neck housing; and a gear train supported in the proximal neck housing, on the pivot pin, and in the distal neck housing, wherein the gear train includes: a proximal gear rotatably supported in the proximal neck housing and being coupled to a distal end of the rotatable drive shaft; an intermediate gear rotatably supported on the pivot pin and being in operative engagement with the proximal gear; a distal gear rotatably supported in the distal neck housing and being in operative engagement with the intermediate gear; and characterised by a pair of output gears (239a, 239b) rotatably supported in the distal neck housing and each being in operative engagement with the distal gear, wherein each output gear defines a coupling socket (239a 1, 239b 1) each configured to selectively receive the drive axle of the end effector. a proximal gear rotatably supported in the proximal neck housing and being coupled to a distal end of the rotatable drive shaft; an intermediate gear rotatably supported on the pivot pin and being in operative engagement with the proximal gear; a distal gear rotatably supported in the distal neck housing and being in operative engagement with the intermediate gear; and characterised by a pair of output gears (239a, 239b) rotatably supported in the distal neck housing and each being in operative engagement with the distal gear, wherein each output gear defines a coupling socket (239a 1, 239b 1) each configured to selectively receive the drive axle of the end effector.