Abstract: A lock mechanism for a closure member, such as a sliding door. The mechanism comprises a housing for securement to the sliding door. A locking slide member is slidingly guided in the housing. The slide member has a locking element to engage and disengage with a keeper member secured to the frame of a door opening adjacent the sliding door. A slide activating rotating knob is rotatably retained in the housing for limited rotating displacement therein. A slide displacing pin is secured to the rotating knob and offset from the central rotating axis of the knob. The slide member has a pin receiving slot which coacts with the pin whereby limited rotation of the knob causes displacement of the pin to frictionally engage the slide in the slot to cause limited sliding displacement of the slide between a locked and unlocked position. The pin and the slide also coact, when in the locked position, whereby to provide positive interlocking to prevent displacement of the slide by force applied thereto.