Three sided architectural scale ruler, imperial size is 12". Laser etched aluminum architectural set square black for architects, students, draftsmen and engineers. Available in various ratios. Small proportions include 1 1/2", 1, 3/4", 3/8", 3/16", 3/32", 1/2", 1/4", 1/8", 3, 16. Large scales include: 1: 10, 1: 20, 1: 30, 1: 40, 1: 50, 1: 60. 12 4/5"L