housing or cavity to retain bolt 220 and compression spring 250 in manner as will now be described in combination with guide member 40 mounted to lug 50 a bolt 220 and a compression spring 250 are retained within the cavity formed by cavities 248 and 54 of guide member 40 and lug 50 respectively with bolt 220 passing through spring 250 in part bolt 220 includes a head portion 222 and a step 224 including a threaded aperture 226 at the end thereof bolt 220 and spring 250 are selected such that the stem 224 of bolt 220 passes through compression spring 250 thus guide member 40 and lug 50 are configured so as to house and constrain movement of spring 250 and bolt 220 particularly the longitudinal movement of bolt 220 within the cavity so formed also illustrated in fig2 b and 3b is a portion of a support frame 290 including a threaded stud 292 threaded stud 292 and internally threaded bolt 220 are selected such that bolt 220 may be tightened upon threaded stud 292 in the usual manner bolt 220 further includes a feature 228 as part of bolt head 222 illustrated as a hexagon shaped aperture so.