Abstract: A folding knife has a blade and a pair of overlying scales all mounted on a pivot post. A lock pin and lock hole on the scales retain them in registry for blade use or storage. A stud on one scale engages a semi-circular slot in the blade and swings it to an extended position during a full turn of the scale around the pivot post, and a corresponding turn in the reverse direction retracts the blade. A blade guard between the scales serves as a stop or abutment for two different parts of the tange of the blade to limit extension and retraction. Spring means are built into the pivot post to yieldingly press the lock pin into the lock hole to prevent unintentional movement.