pass through the web plate aperture 68 the key leg elements 78 will then slidingly engage the keyhole slots 56 from the proximal end 58 and slide downward toward the distal end 60 at the same time the key plate lug 82 will move downward into juxtaposition with the web plate lug 62 such that the padlock holes 64 and 84 through each lug will become generally aligned for installation of a padlock the fastener holes 66 and 86 will also become generally aligned for installation of screws not shown to securely hold the key plate 70 and thereby the instrument 9 onto the support member 42 the support member flanges 44 are juxtaposed against the intermediate member flanges 28 in a partly overlapping position as shown in fig1 the support member flanges 44 and the intermediate member flanges 28 include a second arcuate slot 88 having a second arc center the second arcuate slot 88 can be disposed in one or both of the support member flanges 44 or in one or both of the intermediate member flanges 28 or in all four flanges a second pivotal means is provided for pivotal attachment of the support member flanges 44 to the intermediate member flanges 28 typically the second pivotal means includes a second pivot fastener 90 which is shown as two screws with washers the second pivot fastener 90 pivotally attaches the support member flanges 44 to the intermediate member flanges 28 at the second arc center in this manner the support member 42 will be pivoted in a second plane parallel to the flanges 44 and generally perpendicular to the first plane as shown by arrow 94 in fig5 a second locking fastener 92 slidingly engages the.