Abstract: A freely rotatable disk formed with projections is held in a given position by a spring. The projections and the notches between the projections are selectively engageable by a handle element to deflect the disk, upon operation of the handle element, from its rest position and hold the handle element in an extended position permitting release of a locking bar effecting disengagement with a cooperating locking disk respectively secured to stringer or rail elements of a ladder, to permit the elements to pivot with respect to each other; the spring returning the disk upon movement of the handle to permit engagement of the locking bar, so that the disk, in one position, securely holds the handle and prevents spurious unlocking of the locking bar, and holds the handle in lock-release position to permit free pivoting of the ladder rail or stringer elements when in another position.