A surgical stapling instrument, comprising: a first side; a second side; a longitudinal axis; a first housing portion, comprising: a staple cartridge attachment portion configured to operably support a staple cartridge; and a first lock rail extending from the first housing portion and along said longitudinal axis; a second housing portion, comprising: a jaw member configured to operably support an anvil configured to deform staples deployed from the staple cartridge; and a second lock rail extending from the second housing portion and along said longitudinal axis, wherein each of the first and second lock rails (2131, 2132) includes an inner surface facing the other lock rail and an outer surface facing away from the other lock rail; a pusher bar configured to move a staple driver relative to said staple cartridge attachment portion and said jaw member; and an actuator configured to receive a force thereto, wherein said actuator is configured to be moved between a first position and a second position, wherein said actuator is configured to be moved along said first side when said actuator is in said first position, wherein said actuator is configured to be moved along said second side when said actuator is in said second position, and wherein said actuator further comprises a channel configured to receive said first lock rail and said second lock rail; wherein said channel comprises first and second bearing surfaces (2135, 2136) facing one another and on opposite sides of the channel, wherein the first bearing surface is positioned adjacent to the outer surface of said first lock rail and the second bearing surface is positioned adjacent to the outer surface of said second lock rail, whereby said first bearing surface and said second bearing surface are configured to limit relative movement between said first lock rail and said second lock rail. a first side; a second side; a longitudinal axis; a first housing portion, comprising: a staple cartridge attachment portion configured to operably support a staple cartridge; and a first lock rail extending from the first housing portion and along said longitudinal axis; a staple cartridge attachment portion configured to operably support a staple cartridge; and a first lock rail extending from the first housing portion and along said longitudinal axis; a second housing portion, comprising: a jaw member configured to operably support an anvil configured to deform staples deployed from the staple cartridge; and a second lock rail extending from the second housing portion and along said longitudinal axis, wherein each of the first and second lock rails (2131, 2132) includes an inner surface facing the other lock rail and an outer surface facing away from the other lock rail; a jaw member configured to operably support an anvil configured to deform staples deployed from the staple cartridge; and a second lock rail extending from the second housing portion and along said longitudinal axis, wherein each of the first and second lock rails (2131, 2132) includes an inner surface facing the other lock rail and an outer surface facing away from the other lock rail; a pusher bar configured to move a staple driver relative to said staple cartridge attachment portion and said jaw member; and an actuator configured to receive a force thereto, wherein said actuator is configured to be moved between a first position and a second position, wherein said actuator is configured to be moved along said first side when said actuator is in said first position, wherein said actuator is configured to be moved along said second side when said actuator is in said second position, and wherein said actuator further comprises a channel configured to receive said first lock rail and said second lock rail; wherein said channel comprises first and second bearing surfaces (2135, 2136) facing one another and on opposite sides of the channel, wherein the first bearing surface is positioned adjacent to the outer surface of said first lock rail and the second bearing surface is positioned adjacent to the outer surface of said second lock rail, whereby said first bearing surface and said second bearing surface are configured to limit relative movement between said first lock rail and said second lock rail.