keeper 30 of the present invention consist of any durable and rigid material including but not limited to plastic materials such as polyamide nylon polyethylene polychloropene polyvinyl chloride polyester polypropylene polystyrene polytetrafluoro ethene and polyurethane and the like more preferably the material consists of thermosetting plastics for example resins melamine polyester bakelite u00ae and the like the coil spring 46 consists of an elastic resilient material including but not limited to metals referring to fig4 a to 4c and 10 the mounting plate 40 is shown in greater detail it includes centrally located post 56 protruding from bushing 57 the mounting plate 40 also includes on opposing sides a pair of ramp areas 104 each located proximate to the projected recesses 60 the ramp areas 104 facilitate sliding of the cap member tabs 98 over the raised portion of the projected recesses 60 for tight coupling engagement between the tabs 98 and the projected recesses 60 it is also noted that the screw holes 42 are countersunk for setting the heads of the screws flush with the bearing surface 4 of the mounting plate 40 referring to fig5 a 5 b and 10 the spool member 50 is illustrated in greater detail the top surface of the first flange 66 includes a circular ridge 81 to provide a bearing surface that cooperates with the bearing surface 54 of mounting plate 40.