Abstract: A new attachment plate is provided for securing components of panel assemblies to a mounting post, the attachment plate incorporating a securing hook together with a locking tab. The attachment plate includes a projecting hook which mates with a slot in a mounting post structural member. The hook is of a lesser length than the slot in the post, and a further projection as a locking tab is provided on the attachment plate which also enters the slot and restrains reversed relative movement between the plate hook and the post slot, so as to limit or prevent undesired disassembly of a panel from the post. The application of an upward impact to the plate causes a cam surface on the locking tab to contact the upper end of the mounting post slot. This deflects the locking tab out from the slot, to enable removal of the hook from the slot, for panel disassembly from the post. Also provided is a hooked supporting plate incorporating pairs of flexible presser tabs, to compensate for manufacturing tolerances.