These are practically the same type as Long Ladders, plus mechanical devices permit fastening two or three long ladders together, one atop of the other to make them one extremely long ladder. The two-section ladders reach from 20 to 40 feet. The three-section ladders reach from 30 to 60 feet. Some extension ladders have small wheels set into the side-rails at the top of the upper section. These permit the upper ends of the ladder to roll up freely against the side of the house as it is being raised from below.