Abstract: The knife of the invention comprises a handle including a pair of side scales held in spaced parallel relation by a pair of end pins and a center pin, to provide a narrow elongate channel, a single folding blade pivoted on the forward end pin and a rigid locking rocker arm pivoted on the center pin for rocking movement in the channel. The blade has a key notch in the back of the tang and the forward end of the rocker arm has a key to engage the notch and lock the blade in extended position. An aperture through the aft portion of the rocker arm cooperates with the side scales to form a totally enclosed pocket through which the aft end pin passes, and a spring totally enclosed within the pocket engages the pin and the wall of the aperture to urge the arm into locking position. A recess in the back of the handle facilitates pressing the aft portion of the arm inward to release the blade for retraction. The totally enclosed pocket excludes dirt and ensures positive operation of the spring.