A surgical stapling apparatus, comprising: a handle portion defining a proximal end and a distal end; a body extending distally from the handle portion; a stapling assembly supported on a distal end of the body; an anvil assembly; a drive screw supported within the handle portion and operably coupled to the anvil assembly, the drive screw defining a threaded aperture and being movable relative to the stapling assembly to move the anvil assembly relative to the stapling assembly between a spaced-apart position and an approximated position; and a tissue gap adjustment mechanism disposed within the handle portion and including: a stop member supported on the drive screw, the stop member including a transverse slot, first and second flanges (255a, 255b) extending proximally and distally of the transverse slot, the stop member configured to abut a stop surface within the handle portion to prevent further proximal movement of the drive screw within the handle portion and set a minimum tissue gap between the anvil assembly and the stapling assembly; an asymmetrical polygonal washer defining an eccentrically positioned aperture and including a plurality of pairs of opposed flat sides (269a-269h), the washer being dimensioned to be positioned between the first and second flanges such that each of the pairs of opposed flat sides (269a-269h) can be selectively positioned between and in engagement with the first and second flanges (255a, 255b); and a set screw configured for insertion through the aperture of the washer and the transverse slot, and into the threaded aperture to fix the stop member relative to the drive screw, wherein the washer is repositionable about the set screw to position a selected pair of the opposed flat sides (269a-269h) between and in engagement with the first and second flanges (255a, 255b), at least two of the pairs of opposed flat sides (269a-269h) when engaged with the first and second flanges (255a, 255b) being spaced to position the aperture of the washer at different longitudinal locations in relation to the transverse slot such that the longitudinal position of the stop member in relation to the drive screw can be selectively varied by positioning a different pair of opposed flat sides (269a-269h) in engagement with the first and second flanges (255a, 255b) to selectively change the minimum tissue gap. a handle portion defining a proximal end and a distal end; a body extending distally from the handle portion; a stapling assembly supported on a distal end of the body; an anvil assembly; a drive screw supported within the handle portion and operably coupled to the anvil assembly, the drive screw defining a threaded aperture and being movable relative to the stapling assembly to move the anvil assembly relative to the stapling assembly between a spaced-apart position and an approximated position; and a tissue gap adjustment mechanism disposed within the handle portion and including: a stop member supported on the drive screw, the stop member including a transverse slot, first and second flanges (255a, 255b) extending proximally and distally of the transverse slot, the stop member configured to abut a stop surface within the handle portion to prevent further proximal movement of the drive screw within the handle portion and set a minimum tissue gap between the anvil assembly and the stapling assembly; an asymmetrical polygonal washer defining an eccentrically positioned aperture and including a plurality of pairs of opposed flat sides (269a-269h), the washer being dimensioned to be positioned between the first and second flanges such that each of the pairs of opposed flat sides (269a-269h) can be selectively positioned between and in engagement with the first and second flanges (255a, 255b); and a set screw configured for insertion through the aperture of the washer and the transverse slot, and into the threaded aperture to fix the stop member relative to the drive screw, a stop member supported on the drive screw, the stop member including a transverse slot, first and second flanges (255a, 255b) extending proximally and distally of the transverse slot, the stop member configured to abut a stop surface within the handle portion to prevent further proximal movement of the drive screw within the handle portion and set a minimum tissue gap between the anvil assembly and the stapling assembly; an asymmetrical polygonal washer defining an eccentrically positioned aperture and including a plurality of pairs of opposed flat sides (269a-269h), the washer being dimensioned to be positioned between the first and second flanges such that each of the pairs of opposed flat sides (269a-269h) can be selectively positioned between and in engagement with the first and second flanges (255a, 255b); and a set screw configured for insertion through the aperture of the washer and the transverse slot, and into the threaded aperture to fix the stop member relative to the drive screw, wherein the washer is repositionable about the set screw to position a selected pair of the opposed flat sides (269a-269h) between and in engagement with the first and second flanges (255a, 255b), at least two of the pairs of opposed flat sides (269a-269h) when engaged with the first and second flanges (255a, 255b) being spaced to position the aperture of the washer at different longitudinal locations in relation to the transverse slot such that the longitudinal position of the stop member in relation to the drive screw can be selectively varied by positioning a different pair of opposed flat sides (269a-269h) in engagement with the first and second flanges (255a, 255b) to selectively change the minimum tissue gap.