Positioning joint for folding ladders

Claim 1

A positioning joint for a folding ladder comprising a first joint member having a tubular portion and two spaced first and second disc portions each having a central bore, a second joint member having a tubular portion and a disc portion with a central bore, the disc portion of the second joint member being disposed between the disc portions of the first joint member and comprising first and second sidewalls, a hollow shaft inserted into the central bores of the disc portions of the first and second joint members, a turning plate between an inner wall of the first disc portion of said first joint member and the first sidewall of the disc portion of the second joint member, said turning plate having a plurality of engaging holes formed in alignment with engaging holes circumferentially distributed in the first disc portion of the first joint member and having an arcuate hole into which a projection on the first disc portion of the first joint member projects, the second disc portion of said first joint member having a plurality of engaging holes formed in a reinforcing rim, said disc portion of the second joint member having a pair of engaging holes in the first sidewall facing the turning plate such that they can align with engaging holes of the turning plate and having a pair of overlapping double holes in the second sidewall such that its radially innermost hole aligns with the engaging hole of said first sidewall, said hollow shaft having a spring about itself by which a central portion of a crank-shaped strip is fixed and having a pair of axially elongated holes, a push knob inserted into said hollow shaft, said push knob having a pin hole into which a pin is inserted in alignment with said axially elongated holes, said crank-shaped strip having a small projection on each end which is adapted to be inserted into said engaging holes of the reinforcing rim and the outer portion of said overlapping double holes and having a pair of large projections formed radially inwardly from said small projections, the large projections each adapted to be inserted into the inner portion of said overlapping double holes and in said engaging hole of the first sidewall of the disc portion of the second joint member and corresponding engaging holes of the turning plate and corresponding engaging holes of the first disc portion of the first joint member, and a spring between said turning plate and the first disc portion of the first joint member.