a compression spring not shown has a shaft portion 110 that extends into the interior of cap 104 rubber plug 108 includes an enlarged head which engages the surface of the bore into which shank 10 extends to keep it compressed thereby urging the rounded end of the metal cap past the lower end 102 of the thread into a stop hole not shown in fig1 for releasably locking the bolt in place for turning the bolt head 108 is preferably provided with a connection such as a square protrusion 112 or hole shown in fig1 for turning the bolt with a wrench or the like disposed between the upper end of shank 10 and the lower end of enlarged head portion 92 is a resilient member for example a ring 114 constructed of a resilient material such as rubber or plastic in a preferred embodiment relatively thin metal washers 116 are disposed between the respective ends of the ring and the opposing surfaces of shank 10 and enlarged head portion 92 axially resilient bolt 90 is assembled by initially placing an elastomeric ring 114 and washer 116 combination onto shaft 94 of head 12 and thereafter shaft 94 is inserted into hole 96 in the shank until recess 98 in the shaft of the.