relative positions in this way a plurality of the elements can be used to build up a staircase or variable height and extent application_number US 60481775 A description referring to fig1 through 7 the numeral 1 designates a one piece molded constructional element or unit of generally l shaped configuration in fig2 element 1 is shown in association with two other identical elements designated 2 upper and 3 lower and the three elements 1 2 and 3 are understood to be associated with a pair of laterally spaced apart stringers 4 only one of which is shown in fig2 and 4 to provide a complete stepped structure or staircase 5 element 1 comprises arms 6 and 7 extending at right angles from each other to constitute the horizontal forwardly extending tread or go and the vertical upwardly extending riser parts respectively of the stepped structure 5 the upper surface 8 of tread 6 is provided with an integrally formed anti slip design 9 molded therein as fig1 shows the lower surface 10 of tread 6 has an integrally formed lower member 11 located near the forward extremity of the tread and projecting therefrom downwardly and toward the forward or front edge of the tread the rear surface 12 of riser 7 has an integrally formed upper member 13 located near the upper extremity of the riser and projecting therefrom rearwardly and toward the top end or edge of the riser the projecting member 11 and 13 are hereinafter described in more detail the tread 6 and riser 7 and the upper projecting member 13 are strengthened by a pair of integrally formed outermost webs 15 located at opposite.