US Patent 7424933 Ladder assemblies

A folding ladder includes a hinge assembly having first and second ladder hinge plates each defining a plate opening and a plurality of locking slots. A housing is associated with the first ladder hinge plate and extends through the plate openings to provide a rotation axis for the plates, and the second plate is operable to rotate relative to the first plate about the rotation axis to selectively align slots of the first and second plates. A key outside the housing selectively engages aligned slots to selectively prevent rotation of the ladder hinge plates about the rotation axis and is operated by a manual rotation member. An extension ladder includes a pair of nested outer and inner ladder rails. Ladder rungs connected between and the inner rails define a plurality of supporting openings and the inner rails include outer bearing surfaces associated with the supporting openings. An extension latch mechanism having a pivoting dog is coupled to an outer rail and engages the supporting openings and outer bearing surfaces to support the ladder in an extended posision.