b located in the top wall 54 and positioned along the major axis of the base member 48 the detents 68 extend inwardly from the top wall 54 and are located adjacent the frusto conical side wall 56 while a pair of detents 68 is shown provided in the top wall 54 it will be understood that only a single detent 68 may be provided in the top wall 54 in an alternative embodiment of the present invention as shown in fig3 a b and 4 a b the twistable locking member 50 is rotatably supported on the base member 48 through a fastening assembly 70 the locking member 50 includes a stepped central bore 72 that is axially aligned with the central bore 64 of the base member 48 in one embodiment the fastening assembly 70 includes a rivet 74 extending through the stepped central bore 72 of the locking member 50 and the central bore 64 of the base member 48 washers 76 78 are located in the central stepped bore 72 of the locking member 50 and in the central cavity 66 of the base member 48 respectively the washer 76 is positioned beneath the head of the rivet 74 and the washer 78 is captured in the central cavity 66 of the base member 48 by a radially outwardly extending flange 80 provided at a remote end of the rivet 74 while a rivet 74 is shown for rotatably mounting the locking member 50 to the base member 48 it will be appreciated that other fastening structures such as a nut and bolt for example are possible as well without departing from the spirit and scope of the present invention.