Abstract: A clamping fixture slides between a pair of guide rails and includes a pressure plate between the guide rails. Lock plates with internal openings for receiving the guide rails are held captive on the pressure plate. An operating bar with stepped ends, one adjacent each locking plate, is deflected by a cam mechanism to incline the lock plates relative to the guide rails, thus wedging the lock plates to prevent further sliding along the guide rails. Return springs are provided to urge the lock plates to an unlocked position when pressure on the operating bar is released. A mixing apparatus using the clamping fixture is also disclosed.