A surgical fastener, such as a stapler, is constructed of a pair of opposed jaws, one of which comprises an anvil and the other of which holds the fastener holder assembly, such as a cartridge, oriented towards the anvil. A clamp bar operable by a lever is longitudinally displaceable to advance the cartridge towards the anvil to clamp the subject matter prior to fastening. The clamp bar rides within a frame which supports the lever and the jaws. A thrust bar is longitudinally displaceable in response to the pivoting of a trigger to operate staple pushing elements within the cartridge to eject the fasteners towards the anvil for engagement with body tissue to be fastened. The thrust bar rides within the clamp bar. A pin is inserted between ends of the jaws to secure the jaws against loss of any portion of the body tissue during the clamping procedure. The pin has a cam surface which moves during a securing of the pin. A lockout system is provided for preventing both clamping and ejection of the fasteners, e.g., staples, until the pin is secured. The lockout system includes a bell crank which blocks movement of the clamp bar during an unsecured state, the crank being operated by a cam follower which rides on the cam surface of the pin. An intermediate link connects the trigger with the thrust bar, the intermediate link riding on the lever to be retracted during blockage of the clamp bar so as to prevent operation of the thrust bar.