A surgical stapling apparatus (10) includes a tissue gap adjustment mechanism (260) having a stop member (250), an asymmetrical polygonal washer (264), and a set screw (262). The stop member (250) is supported on a drive screw (220), includes first and second flanges (255a, 255b), and defines a transverse slot (254) between the flanges (255a, 255b). The stop member (250) sets a minimum tissue gap. The washer (264) defines an eccentrically positioned aperture (268) and includes a plurality of pairs of opposed flat sides (269a-269h). The set screw (262) is configured to fix the stop member (250) relative to the drive screw (220). The washer (264) is selectively rotatable about the set screw (262) to position a selected pair of sides (269a-269h) between and in engagement with the flanges (255a, 255b) to set the position of the aperture (268) of the washer (264) relative to the transverse slot (254), thereby setting the stop member (250) relative to the drive screw (220) and defining the minimum tissue gap.
