Abstract: The foldable blade knife comprises a blade with a tang positioned between the arms of a flat U-shaped handle at the ends of the arms away from the base of the handle, and a pivot pin extends through the arms of the handle and through the tang equidistant from the butt of the tang and the ends of the arms. The handle defines an opening sized and shaped to approximately correspond to the size and shape of the blade element, and at least one edge surface of the tang and the facing surface of an arm of the handle are formed in interfitting convex-concave shapes so that the resilient arms of the handle tend to hold the blade folded into the handle or to hold the blade extending out coextensively from the handle and when the handle is grasped by a hand, the gripping force by the hand tends to further lock the blade in its open or closed positions.

Abstract: The knife has a slotted handle and a blade that pivots into and out of the slot of the handle. A free floating pivot pin extends through the slotted end of the handle and through the opening of the tang of the blade, and a slotted ring lock extends about the pivot pin. The ring lock is rotatable on the handle so that its slot is movable into and out of alignment with the slot of the handle, to lock the blade with respect to the handle. The periphery of the tang defines hemispherical indentations, and a spring-urged ball in the handle engages the tang and registers with the indentations so that the blade resists movement when in its folded or extended positions but is free to move when intermediate the end positions.