Gage blocks, also spelled gauge blocks, are used as a reference for the calibration of measuring equipment in machine shops. Use this gage block set to calibrate your micrometers, sine bars, calipers, and dial indicators for use in inspection. SPI's steel 81-piece rectangular gage block set, model 30-912-0, comes with a fitted case and a certificate of calibration traceable to NIST. Economy-grade shop accuracy provides a measurement tolerance of +/- 0.00005. The gage block size range is 0.05 inches to 4 inches with step increments of 1 inch (4 blocks), 0.05 inch (19 blocks), 0.001 inch (49 blocks), and 0.0001 (9 blocks). 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.