Product Description The Starrett 4" Combination Square with Square Head features a reversible lock bolt, and hardened steel, photo-engraved blade with regular finish. This product also includes a cast iron head with black wrinkle finish. 4", 4R Grad, Regular Blade. The square head has a precision ground 90° square face and a 45° miter face. It is a highly versatile layout tool for scribing right angles and parallel lines, and a measuring tool that can be used as a tri-square, miter, depth gage, height gage, and level. Starrett precision measuring tools have been the standard for high-quality dimensional measuring tools since 1880. The powerful tools meet or exceed the accuracy and performance requirements of national and international standards, and are traceable to the United States National Institute of Standards and Technology. The L.S. Starrett Company, founded in 1880, manufactures more than 5,000 variations of Precision Tools, Gages, Measuring Instruments, and Saw Blades for industrial, professional, and consumer markets worldwide. From the Manufacturer Starrett 11H series Combination Squares consist of a machine divided, hardened and tempered steel rule on which is mounted an adjustable square head. The heads are cast iron with reversible lock bolt and scriber. The value of Starrett Tools is that they are accurate and will last