A surgical instrument having an elongate shaft has a blade assembly 340 which is slideable longitudinally. The blade assembly 340 connects at its proximal end to a collar 348 having first and second components. A tab or protrusion 2102 on the blade assembly 340 fits into a recess 2100 in the inner component to retain the blade assembly 340. The inner component is freely rotatable inside the outer component, such that the blade assembly 340 may rotate with the drive shaft. The outer component connects to a trigger mechanism to provide longitudinal movement to the blade assembly 340 allowing it to be deployed or retracted. The blade assembly 340 is shaped such that it may enter the inner component when presented at an appropriate angle relative to the longitudinal axis, but once rotated into alignment with the axis it is retained in the component.
