Designed for the exacting needs of engineers. Change units quickly and easily by rotating dial at either end of scale. 12" measuring length, exact calibrations. Highest quality aluminum. Adjusts to 10, 20, 40 and 50 parts to the inch. Aluminum Engineers Ruler, 12", Silver. Ruler Type: Triangular Scale; Length: 12"; Material(s): Aluminum; Color(s): Silver.