This innovative design incorporates a precision micrometer drive, ¼-20 mounting hole and removable tube. The slit opens equally from center (fully closed) to 6.0mm (maximum clear opening). Mounted in a black anodized metal housing 55.5mm long x 38.1mm high x 22.2mm thick with a 28mm long x 23mm diameter tube protruding from the face. The tube is threaded into the main body of the slit housing as a light baffel and is removable. Slit length is 6.3mm at center of aperture. A ¼-20 tap hole for mounting is centered in the base. Micrometer-driven for fine adjustment.