where the rails have oval slots 37 along a centerline of the web and the accessories have l hooks 39 the l hooks each have an inner ledge 45 that presses against the web to restrain movement of the hook away from the web the l hooks are inserted into the slots and the accessory is slid along the rail so that the accessory is secured by the ledges on the hooks against movement in all directions but one along the rail a catchment device on the accessory which may be a spring latch or may be a non automatic catch catches a catchment surface on the ladder to secure the accessory the catchment surface may be one of the slots with no hook inserted or it may be a slot into which a hook is inserted such as the bottom most slot in fig3 after the hooks are slid into engagement a portion of the bottom slot that was occupied as the hook was inserted is now available for use a catch 47 as shown in fig3 may be inserted into this empty portion of the slot beside the base of the hook in fig3 the catch 47 is shown in inserted position not in retracted position the catch 47 may be a spring loaded latch or it may be a manually actuated catch in the oval slot system shown in fig3 because the slots are symmetrical up and down any accessory can be attached in either an up orientation or a down orientation which is an advantage for accessories.