Abstract: A housing is provided including peripherally extending side walls and a fixed wall extending between one set of corresponding marginal portions of the side walls. The side of the housing opposite the fixed wall is open and a cover is provided for the open side of the housing. The cover and housing include structure operable to releasably lock the cover in a closed position. At least one of the side walls has a slot formed therein opening through the free edge thereof remote from the fixed wall and a link chain section composed of interconnected links includes at least one link intermediate the opposite ends of the link chain section which may be received through the slot. The chain section and the portions of the one side wall defining the slot include coacting structure preventing longitudinal displacement of the chain section through the slot.