An actuation mechanism for actuating an electromechanical end effector, the actuation mechanism comprising: a housing having a first screw and a second screw each rotatably disposed therein; and a shaft assembly extending distally from within the housing, the shaft assembly including: a shaft axially movable relative to the housing and configured to be coupled to an electromechanical end effector; a first hub including: a first portion having the shaft secured therein; and a second portion connected to the first portion and having an inner surface having the first screw threadedly connected thereto such that rotation of the first screw moves the first hub to effect longitudinal movement of the shaft; a longitudinal knife bar axially movable relative to the shaft and configured to be coupled to a knife blade of an electromechanical end effector; and a second hub including: a first portion having the shaft movably received therein, the first portion being connected to the longitudinal knife bar; and a second portion connected to the first portion of the second hub and having an inner surface having the second screw threadedly connected thereto such that rotation of the second screw moves the second hub to effect axial movement of the longitudinal knife bar. a housing having a first screw and a second screw each rotatably disposed therein; and a shaft assembly extending distally from within the housing, the shaft assembly including: a shaft axially movable relative to the housing and configured to be coupled to an electromechanical end effector; a first hub including: a first portion having the shaft secured therein; and a second portion connected to the first portion and having an inner surface having the first screw threadedly connected thereto such that rotation of the first screw moves the first hub to effect longitudinal movement of the shaft; a longitudinal knife bar axially movable relative to the shaft and configured to be coupled to a knife blade of an electromechanical end effector; and a second hub including: a first portion having the shaft movably received therein, the first portion being connected to the longitudinal knife bar; and a second portion connected to the first portion of the second hub and having an inner surface having the second screw threadedly connected thereto such that rotation of the second screw moves the second hub to effect axial movement of the longitudinal knife bar. a shaft axially movable relative to the housing and configured to be coupled to an electromechanical end effector; a first hub including: a first portion having the shaft secured therein; and a second portion connected to the first portion and having an inner surface having the first screw threadedly connected thereto such that rotation of the first screw moves the first hub to effect longitudinal movement of the shaft; a first portion having the shaft secured therein; and a second portion connected to the first portion and having an inner surface having the first screw threadedly connected thereto such that rotation of the first screw moves the first hub to effect longitudinal movement of the shaft; a longitudinal knife bar axially movable relative to the shaft and configured to be coupled to a knife blade of an electromechanical end effector; and a second hub including: a first portion having the shaft movably received therein, the first portion being connected to the longitudinal knife bar; and a second portion connected to the first portion of the second hub and having an inner surface having the second screw threadedly connected thereto such that rotation of the second screw moves the second hub to effect axial movement of the longitudinal knife bar. a first portion having the shaft movably received therein, the first portion being connected to the longitudinal knife bar; and a second portion connected to the first portion of the second hub and having an inner surface having the second screw threadedly connected thereto such that rotation of the second screw moves the second hub to effect axial movement of the longitudinal knife bar.