A surgical instrument (10) comprising a handle assembly (12), a body (14), a tool assembly (17) and an articulation assembly (420) is disclosed. The articulation mechanism (420) includes a receptacle (436), and a main shaft (432). A lower clutch (430) is fixedly positioned within the receptacle and has a serrated portion (444) including a plurality of serrations (448,450). An upper clutch (428) includes at least one projection (470) positioned to engage the serrations of the lower clutch to releasably retain the main shaft at a rotatably fixed position. An angle between a first pair of adjacent serrations is defined as a first angle, an angle between a second pair of adjacent serrations is defined as a second angle, and an angle between a third pair of adjacent serrations is defined as a third angle. The first angle, the second angle, and the third angle are each different from one another.
