could also be used on the narrow steps 50 but it is believed that additional locks are not needed there and the narrowness of step 50 provides less space for mounting of an interlock mechanism a complementary type locking mechanism is used so that opposite edges of the steps 60 have the opposite types of mechanisms for example the preferred embodiment of the present invention uses complementary hook and eye members as the interlock although other types of complementary latching members could also be used for the orientation in fig9 steps 60 would have their hooks along one edge and their eyes along their opposite edge so that the correct complementary locking members of adjacent stages would be positioned adjacent one another however in the orientation of fig8 because step 60 on section 121 is reversed left to right it would be necessary to reverse or interchange its locking means also or those of the adjacent sections 120 122 so that the correct complementary locking members will be adjacent one another for this purpose the present invention provides a locking means that can be quickly converted from one to the other type of the complementary locking means in the preferred embodiment this means that the lock can be converted from a hook type to an eye type as necessary as seen in fig6 and 11 plates 130 are secured by suitable means for example screws to the.