Surgical stapling instrument with an articulating end effector

A surgical instrument including a shaft assembly and an end effector, where the end effector can be moved relative to the shaft assembly. The shaft assembly can include a lock member selectively engageable with the end effector to limit, or prevent, relative movement therebetween. In at least one embodiment, the end effector can include a lock member having a plurality of teeth and/or a plurality of recesses, where the shaft assembly lock member can engage the teeth and/or recesses to fix the relative position between the end effector and shaft assembly. In various embodiments, the teeth can be positioned between first and second surfaces of the end effector lock member to reduce the possibility that the teeth can impinge on soft tissue surrounding the lock member. In other embodiments, the teeth can be beveled in order to allow the teeth to slide relative to the soft tissue.