A torque nut with an axially deformable projection protruding from the axially inner end face of the torque nut. Metal ions in the active layer bind to the nitrogen thereof, enhancing retention of the metal ions in the active layer for improved, stable data retention. The reed switch may be encapsulated in a material and placed in a cavity in one side of the cradle or may be located in the front wall or a separate place in close proximity to the cradle.