An adapter assembly (100, 300, 400) for operably connecting an end effector to a surgical instrument, the adapter assembly comprising: a proximal end for operable connection to the surgical instrument and a distal end for operable connection to an extension assembly configured for selective engagement with the end effector; a drive coupling assembly and a drive transfer assembly operably connected to the drive coupling assembly, the drive transfer assembly including a support plate disposed within a housing, the support plate being rotationally fixed to the housing and having a distal side and a proximal side; a first proximal shaft including a first gear assembly, a portion of the first proximal shaft extending through an aperture in the support plate and the first gear assembly being on the distal side of the support plate; a second proximal shaft defining a longitudinal axis and having a distal portion extending through a second aperture in the support plate, the second proximal shaft including a second gear assembly on the proximal side of the support plate; a first distal shaft disposed along the longitudinal axis ("Z") and including a third gear assembly on the distal side of the support plate, the first gear assembly being mechanically engaged with the third gear assembly such that rotation of the first gear assembly causes rotation of the third gear assembly in an opposite direction; and a second distal shaft including a fourth gear assembly on the proximal side of the support plate, the second distal shaft having a portion that extends through a third aperture of the support plate, the second gear assembly being mechanically engaged with the fourth gear assembly such that rotation of the second gear assembly causes rotation of the fourth gear assembly in an opposite direction, wherein the distal portion of the second proximal shaft is disposed at least partially within an internal cavity of the third gear assembly. a proximal end for operable connection to the surgical instrument and a distal end for operable connection to an extension assembly configured for selective engagement with the end effector; a drive coupling assembly and a drive transfer assembly operably connected to the drive coupling assembly, the drive transfer assembly including a support plate disposed within a housing, the support plate being rotationally fixed to the housing and having a distal side and a proximal side; a first proximal shaft including a first gear assembly, a portion of the first proximal shaft extending through an aperture in the support plate and the first gear assembly being on the distal side of the support plate; a second proximal shaft defining a longitudinal axis and having a distal portion extending through a second aperture in the support plate, the second proximal shaft including a second gear assembly on the proximal side of the support plate; a first distal shaft disposed along the longitudinal axis ("Z") and including a third gear assembly on the distal side of the support plate, the first gear assembly being mechanically engaged with the third gear assembly such that rotation of the first gear assembly causes rotation of the third gear assembly in an opposite direction; and a second distal shaft including a fourth gear assembly on the proximal side of the support plate, the second distal shaft having a portion that extends through a third aperture of the support plate, the second gear assembly being mechanically engaged with the fourth gear assembly such that rotation of the second gear assembly causes rotation of the fourth gear assembly in an opposite direction, wherein the distal portion of the second proximal shaft is disposed at least partially within an internal cavity of the third gear assembly.