A shaft assembly (6000) is disclosed which comprises a shaft, an end effector (1300) rotatably connected to the shaft about an articulation joint, and an articulation driver (1440,1450) configured to rotate the end effector (1300) about the articulation joint. The end effector (1300) further comprises a first articulation lock (6496) configured to engage the end effector (1300) and a second articulation lock (6494) configured to engage the articulation driver (1440,1450) which co-operatively prevent the end effector (1300) from rotating relative to the shaft, when actuated. The actuation and/or de-actuation of the first articulation lock (6496) and the second articulation lock (6494) can be contemporaneous or, in certain instances, staggered.
