support legs 24 include a base end 80 and a pivot arm 82 fig6 and 7 also illustrate a pivot stop 84 the pivot stop 84 as illustrated in fig6 has a pad 85 that engages the base 80 and a disengageable pad 86 that is locked under the pivot arm 82 the pivot arm 82 may be attached to the rail 80 at a pivot location 87 the pivot stop 84 is supported in a pivotal manner at 88 there is also included a slide ring 89 attached to the pivot arm 82 in fig6 the slide ring 89 is shown at its uppermost position with the pivot arm 82 pivoted and locked in position so that the support legs 24 are in an upright position such as the position illustrated also in fig1 in order to pivot the support legs 24 to a downward position reference may now be made to fig7 for that purpose the pad 86 may be screwed down so as to disengage from the pivot arm 82 allowing the pivot arm 82 to pivot this causes the slide ring 89 to slide along the base 80 to its lowermost position as illustrated in fig7 this pivoting action.