Twist-Proof due to the Alflo rung joints. Slip-resistant Traction-Tred D-rungs. Strong modified I-beam rails. Interlocking side rails. Smooth operating pulley. Mar-resistant molded end caps. Shoe rest flat or is held in spur position with shu-lok feature.Spring loaded locks operate smoothly U.L. Listed and labeled. Meets ANSI Code and OSHA requirements. Dimensions: Side rails 3 in wide; Flange 1 in wide; Rungs 1-3/4 in wide; Base width 17-3/8 in outside rails. Length of extension ladders when not extended is half the total length of the sections.