A surgical fastener apparatus comprising: a handle; an end effector operably coupled to said handle, said end effector comprising: an elongated channel configured to support a cartridge therein; an anvil movably supported on said elongated channel for selective movement toward said elongated channel to a closed position and away from said elongated channel to an open position; an actuator member movably supported within said elongated channel and selectively movable from an unactuated proximal position to actuated positions within said elongated channel, wherein the apparatus is characterised in that: said anvil further comprises an elongated slot therein; said actuator member comprises: a lower actuator portion slidably engaging said elongated channel; an upper actuator portion configured to protrude into said elongated slot; and a retainer member protruding from each lateral side of said upper actuator portion in a direction that is transverse to said elongated slot in said anvil; and a height adjustment member on each said retainer member, or on said anvil adjacent each lateral side of said elongated slot for confronting relationship with said retainer members, to selectively adjust a spacing between said anvil and said elongated channel when said anvil is in said closed position in response to electrical current applied thereto. a handle; an end effector operably coupled to said handle, said end effector comprising: an elongated channel configured to support a cartridge therein; an anvil movably supported on said elongated channel for selective movement toward said elongated channel to a closed position and away from said elongated channel to an open position; an actuator member movably supported within said elongated channel and selectively movable from an unactuated proximal position to actuated positions within said elongated channel, wherein the apparatus is characterised in that: said anvil further comprises an elongated slot therein; said actuator member comprises: a lower actuator portion slidably engaging said elongated channel; an upper actuator portion configured to protrude into said elongated slot; and a retainer member protruding from each lateral side of said upper actuator portion in a direction that is transverse to said elongated slot in said anvil; and a height adjustment member on each said retainer member, or on said anvil adjacent each lateral side of said elongated slot for confronting relationship with said retainer members, to selectively adjust a spacing between said anvil and said elongated channel when said anvil is in said closed position in response to electrical current applied thereto. an elongated channel configured to support a cartridge therein; an anvil movably supported on said elongated channel for selective movement toward said elongated channel to a closed position and away from said elongated channel to an open position; an actuator member movably supported within said elongated channel and selectively movable from an unactuated proximal position to actuated positions within said elongated channel, wherein the apparatus is characterised in that: said anvil further comprises an elongated slot therein; said actuator member comprises: a lower actuator portion slidably engaging said elongated channel; an upper actuator portion configured to protrude into said elongated slot; and a retainer member protruding from each lateral side of said upper actuator portion in a direction that is transverse to said elongated slot in said anvil; and a height adjustment member on each said retainer member, or on said anvil adjacent each lateral side of said elongated slot for confronting relationship with said retainer members, to selectively adjust a spacing between said anvil and said elongated channel when said anvil is in said closed position in response to electrical current applied thereto. said anvil further comprises an elongated slot therein; said actuator member comprises: a lower actuator portion slidably engaging said elongated channel; an upper actuator portion configured to protrude into said elongated slot; and a retainer member protruding from each lateral side of said upper a lower actuator portion slidably engaging said elongated channel; an upper actuator portion configured to protrude into said elongated slot; and a retainer member protruding from each lateral side of said upper actuator portion in a direction that is transverse to said elongated slot in said anvil; and a height adjustment member on each said retainer member, or on said anvil adjacent each lateral side of said elongated slot for confronting relationship with said retainer members, to selectively adjust a spacing between said anvil and said elongated channel when said anvil is in said closed position in response to electrical current applied thereto.