The present invention relates to automatic rechargeable rodent kill traps, and more specifically to the present invention relates to a piston unit for an automatic rechargeable mechanical trap comprising a piston, and a piston bore. The piston bore comprises a1) a threaded cylindrical rod adapted to rotate around its central axis within the piston bore cavity wherein the first end of the threaded cylindrical rod is adapted for engagement with a motor unit, and wherein the second end is a free end b1) a spring positioned within the piston bore cavity, and around or alongside the threaded cylindrical rod and c1) a lock plate comprising i) a threaded opening configured for receiving the threaded cylindrical rod and ii) a protrusion extending radially away from the threaded opening. The piston comprises a2) a central channel adapted for receiving the threaded cylindrical rod, and wherein the upper part of the central channel further comprises a recess configured for receiving a protrusion of the lock plate. The bottom part of the recess comprises a cavity configured for receiving said protrusion of the lock plate in a locking configuration when the lock plate is rotated around the central axis of the threaded cylindrical rod.
