A surgical end effector, comprising: a first jaw comprising a channel, wherein a plurality of slots (1214, 1217) are defined in said channel, and wherein said plurality of slots (1214, 1217) comprises: a pivot pin slot comprising an arcuate portion and a locking portion; and a slide pin slot; a second jaw adapted to pivot relative to the first jaw, comprising: an anvil; and a mounting portion comprising a pivot pin, wherein said pivot pin is movably positioned in said pivot pin slot and moves along said arcuate portion when said second jaw pivots relative to said first jaw; wherein said locking portion of said pivot pin slot is configured to prevent movement of said pivot pin along said arcuate portion when said pivot pin is positioned within the locking portion, thereby preventing the second jaw from pivoting relative to the first jaw; characterized in that: a slidable firing bar guide is positioned in said first jaw, wherein said slidable firing bar guide comprises: a body comprising a slide pin, wherein said slide pin is movably positioned in said slide pin slot; and a leg (1241, 1248) extending proximally from said body, wherein said leg (1241, 1248) longitudinally overlaps said locking portion of said pivot pin slot when said slide pin is positioned within a range of positions in said slide pin slot, thereby preventing said pivot pin from being positioned within said locking portion, and wherein said leg (1241, 1248) is longitudinally offset from said pivot pin slot and does not overlap said locking portion of said pivot pin slot when said slide pin is positioned outside said range of positions in said slide pin slot. a first jaw comprising a channel, wherein a plurality of slots (1214, 1217) are defined in said channel, and wherein said plurality of slots (1214, 1217) comprises: a pivot pin slot comprising an arcuate portion and a locking portion; and a slide pin slot; a pivot pin slot comprising an arcuate portion and a locking portion; and a slide pin slot; a second jaw adapted to pivot relative to the first jaw, comprising: an anvil; and a mounting portion comprising a pivot pin, wherein said pivot pin is movably positioned in said pivot pin slot and moves along said arcuate portion when said second jaw pivots relative to said first jaw; an anvil; and a mounting portion comprising a pivot pin, wherein said pivot pin is movably positioned in said pivot pin slot and moves along said arcuate portion when said second jaw pivots relative to said first jaw; wherein said locking portion of said pivot pin slot is configured to prevent movement of said pivot pin along said arcuate portion when said pivot pin is positioned within the locking portion, thereby preventing the second jaw from pivoting relative to the first jaw; characterized in that: a slidable firing bar guide is positioned in said first jaw, wherein said slidable firing bar guide comprises: a body comprising a slide pin, wherein said slide pin is movably positioned in said slide pin slot; and a leg (1241, 1248) extending proximally from said body, wherein said leg (1241, 1248) longitudinally overlaps said locking portion of said pivot pin slot when said slide pin is positioned within a range of positions in said slide pin slot, thereby preventing said pivot pin from being positioned within said locking portion, and wherein said leg (1241, 1248) is longitudinally offset from said pivot pin slot and does not overlap said locking portion of said pivot pin slot when said slide pin is positioned outside said range of positions in said slide pin slot. a body comprising a slide pin, wherein said slide pin is movably positioned in said slide pin slot; and a leg (1241, 1248) extending proximally from said body, wherein said leg (1241, 1248) longitudinally overlaps said locking portion of said pivot pin slot when said slide pin is positioned within a range of positions in said slide pin slot, thereby preventing said pivot pin from being positioned within said locking portion, and wherein said leg (1241, 1248) is longitudinally offset from said pivot pin slot and does not overlap said locking portion of said pivot pin slot when said slide pin is positioned outside said range of positions in said slide pin slot.