Abstract: A locking mechanism for holding a selected blade or tool kit of a multi-purpose folding tool in an extended position. A base portion of each blade is mounted on a pivot pin mounted in a tool handle. The base portion includes a cam and a notch, and a spring included in the handle biases a flange against the cam and urges the flange into the notch to hold the selected blade in an extended position. The notch has a sharp lip and the flange is attached to the spring by a bend formed in a way leaving effectively a zero radius of curvature inside the bend. As a result, the lip of the notch and the inside corner surface of the bend defining the flange do not interact as cam and follower to urge the flange out from the notch, and a shorter flange and shallower notch are effective to lock the blade in position. A channel which receives and holds blades in a folded configuration of the tool has inside corners between sidewalls and a base, each corner having effectively a zero radius of curvature.