A radio communication system by which an additional terminal can be easily registered to group information to set up radio communication between particular terminals, and a new user can conduct radio communication in a short period of time. The probe includes first and second conductors disposed in a sheath, and first and second electrodes electrically insulated from the sheath and protruding from its distal end. The air vent and damper system of the invention allows the apparatus to operate at peak efficiency regardless of the number of pallets present in the apparatus. A tapered die is pressed into the bottom of the piling to expand the lower end of the piling outwardly such that it extends into the intermediate portion of the friction collar.