An instrument includes a body having an interior conduit. A shaft extends distally out of the body and is movable between a retracted position and an extended position. A locking mechanism that selectively secures the shaft in the retracted and extended positions includes grooves in the body and a locking nut having pins that travel through the grooves to move the locking nut between a locked position and an unlocked position. The locking mechanism also includes compression flanges that flex towards and apply pressure/friction to the shaft when the locking nut is in the locked position and release/reduce the pressure/friction from the shaft when the locking nut is in the unlocked position. The compression flanges restrict the movement of the shaft when the compression flanges are flexed towards, and apply pressure to the shaft.
