The present disclosure provides for a loading unit for use with and/or supportable on a distal end of a surgical stapling apparatus. The loading unit includes a housing portion including a distal end and a proximal end, a drive assembly slidably supported within the housing portion of the loading unit, and a locking mechanism pivotally supported on the housing portion of the loading unit, the locking mechanism having a first position wherein the locking mechanism engages a portion of the drive assembly and maintains the position, preferably the axial position, of the drive assembly relative to the housing portion of the loading unit, and the locking mechanism having a second position wherein the locking mechanism disengages the drive assembly and enables the drive assembly to move relative to the housing portion.