A surgical fastener applying apparatus comprising an elongated body portion having proximal and distal portions, and a head portion disposed adjacent the distal portion of the elongated body portion, the head portion including a shell assembly including one or more annular rows of surgical fasteners, a first tissue contact surface defining a plurality of slots through which the surgical fasteners are ejected during firing of the surgical fastener applying apparatus, and an anvil retainer including a raised boss and an anvil assembly movable in relation to the shell assembly between spaced apart and approximated positions, the anvil assembly including an anvil head (120'), a second tissue contacting surface, and a center rod (154') extending proximally from the anvil head, the center rod including a proximal portion, a distal portion, and a central portion interposed between the proximal and distal portions, the center rod including an annular protrusion (280') configured for releasable engagement with the anvil retainer, and an interference rib (290') configured to enhance frictional engagement of the center rod with the shell assembly, the interference rib configured to engage the raised boss of the anvil retainer.
