A connection portion for attaching a disposable loading unit (5502) to the shaft (5520) of a surgical instrument. The connection portion can include a rotatable collar (5580), which can be rotated relative to the disposable loading unit (5502) and the shaft (5520). The connection can include a spring (5592) for biasing the collar (5580) and/or the disposable loading unit (5502) into a locked orientation.