member 78 in between its guide edges 92 and 94 it will be appreciated especially when viewing fig6 that the outer peripheries 100 and 102 respectively of the first and second members 76 and 78 are both contoured so as to approximate the inner surface of the tubular cross bar 12 and that the cross section of the combined members 76 and 78 substantially fills up the hollow space inside the tubular cross bar 12 in the wall of the bore 80 formed in the second elongated guide member 78 there is provided a channel 104 which is designed to accommodate therein the rib 74 of the lock cylinder 72 securing thereby the lock cylinder 72 in and to the surrounding second guide member 78 due to the combined effects of the rib 74 extending into the channel 104 of the member 78 both the lock cylinder 72 and the elongated guide member 78 are secured to one another as well as within the cross bar 12 against displacement therein by inserting and turning a key not shown into the lock cylinder 72 in a way identical to that shown in and described with reference to fig1 4 the first dead bolt member 76 is caused to be displaced axially between its first operative position illustrated in fig6 extending into the transverse cut.