Twist-Proof due to the Alflo rung joints. Mar-resistant molded end caps and rail closures. Traction-Tred deeply serrated flat steps. Easy to grip modified I-beam siderails. Smoothly operating extruded aluminum double rung locks. Shoe pivots to allow the shoe pad full ground contact for slip-resistance. Equipped with rope and smooth operating pulley except for No. D1116-2. U.L. Listed. Meets ANSI Code and OSHA requirements. Dimensions: Siderails 2-3/4" wide (16' and 20') 3" wide (24' to 28'); Flange 15/16" wide; Rungs 1- 1/2" wide; Base width 16" outside rails. Length of extension ladders when not extended is half the total length of the sections