Use these ultra precision angle blocks for production and inspection applications. Each block is 3 inches long by 1/4 inch thick, made from precision-ground hardened steel. Angular accuracy of 0.0001 inch, +/-30 arc seconds. Includes 17 blocks plus two riser blocks: 1/4°, 1/2°, 1°, 2°, 3°, 4°, 5°, 10°, 15°, 20°, 25°, 30°, 35°, 40°, and 45°. 17 block set includes fitted case. This set is not serialized and does not include NIST-traceable certification. For over 60 years, SPI has introduced innovative products to the metalworking and laboratory industries. SPI measuring instruments are durable, precise, and reliable — all backed by an industry-leading 2-year warranty.