An instrument includes a body having an interior conduit and a conductor extending within the interior conduit. A shaft extends distally out of the body and is movable between a retracted position and an extended position. A sliding conductor extends within the shaft and a contact portion of the sliding conductor extends between the conductor of the body and an exterior portion of the shaft. An end portion of the contact portion is at least partially disposed within an opening of the shaft. A locking mechanism that selectively secures the shaft in the retracted and extended positions includes a locking nut that is selectively movable between a locked position and an unlocked position and compression flanges with contact pads that flex toward the shaft when the locking nut is in a locked position to secure the shaft in the extended or retracted positions.