Patent ID: 7341392

Claim:
An articulated joint for a foldable ladder comprising: an outer casing pair with two opposite outer casing shells each having a guide slot and one of the outer casing shells providing a spring seat with a pinhole at the inner side thereof under the guide slot; an inner casing pair with two opposite inner casing shells being disposed in the outer casing part and the respective inner casing shell having three locating recesses being provided at a circumferential side of thereof; and a lock block set further comprising an elongated lock block, a fixing pin and a spring, the lock block having a bottom side with a locating hole at the center of the bottom side for being joined to a first end of the fixing pin, another end of the fixing pin passing through the pinhole, and the spring being disposed between the lock block and a spring seat to surround the pinhole; characterized in that two triangular prism shaped projections are formed on each of two long edges of the bottom side of the lock block, respectively in a way of a distance from the respective projection to a neighboring short edge of the bottom side of the lock block being equal to a thickness of the respective outer casing shell such that both ends of the lock block are capable of being received in the guide slot respectively with an outwardly facing end of the respective projection keeping contact with the inner sides of the outer casing shells.