Abstract: A foldable knife (20) having a mechanism (29) whick locks its blade (21) in open position but not in its closed position within a pocket (27) formed in its sheath (22). Mechanism (30) is mounted at a pivot axis for the rotation of sheath (22) to blade (21), and comprises a body (31) eccentrically mounted to an axle (30), the block body (31) being releasably slidable into either an opening (44) formed in the thickness of blade (23) or into a position straddling opening (45) and a cavity (44) formed in handle side (23). When so straddled, the blade is locked in open position. A pin (38) mounted on axle (30) is depressed against the biasing of a spring (39) mounted to the other side of block body (31), to push it from its straddling position, so that it slides into the thickness of blade (21), whereby sheath (22) of knife (20) is rotatable about blade (21) to place the latter in its pocket (27).