Collapsible ladder

A collapsible ladder comprising:

• a plurality of tubular rungs;
• side support members pivotally connected between each end of adjacent rungs, each side support member comprising a pair of pivotally interconnected tubular links each having a length less than half of that of the rungs;
• said links having a generally square cross-section for providing ends with flat surfaces defining a contacting region for contacting the flat surface of an adjacent pivotally interconnected link, and wherein the area of the contacting region of the links is from 20 to 35% of the surface area of one side of the link;
• pin receiving apertures passing through opposite wall portions of the tubular rungs and the tubular links near the ends thereof;
• pivotal connecting means comprising a first pivot pin disposed in the aperture of each adjacent pair of the interconnected links that define said support member, and a second pivot pin disposed in the aperture of each end of each of the rungs and the aperture of at least one of said side support members;
• said apertures and pivot pins being disposed inwards from the ends of the links to define support arms outward from the pin, said support arms having bearing surfaces that bear on the adjacent link for providing rigidity of the pivotally interconnected links, about an axis passing transversely through the pivot pin and parallel with the rungs, when the ladder is in an deployed condition;
• and
• compression applying fastener means associated with at least some of said pins for pressing the contacting regions of the links against one another with a force sufficient to provide a frictional force upon pivoting of said links for restricting the deployment rate of the ladder, and the compression force applied by the fastener is greater than 0.05 pounds per square inch.