The 3520 Aluminum 20' Extension Ladder has a duty rating of 225 pounds and interlocking side rails. The D-rungs are slip resistant, and the heavy-duty spring-loaded locks operate smoothly. Slipping is not a concern with spur position shoe holds, including a swiveling feature for versatility. Mar-resistant end caps help to protect the surface the ladder is leaning against. The exclusive three piece rung-to-rail connection means twist-proof performance every time.