US Patent 10246939 Folding and rigid ladder with extensions

An extension module is provided for attachment to a folding or rigid ladder to extend the effective working height of the ladder. A ladder that is designed for use with an extension module according to the invention defines the base module to which the extension module is attached. Cooperatively constructed interconnecting structures on the ladder and the extension module operate to secure the extension module to the ladder and to stabilize the combination of the ladder with the extension.