38-piece precision gauge block set: Includes Grade 0 and Grade 1 blocks for measurement, calibration, and inspection. Strict tolerance control: Each block meets national or international metrology standards for dimensional accuracy. Premium hardened steel construction: Offers excellent wear resistance and durability for lab and industrial use. Versatile size range: Covers essential lengths with stackable combinations for flexible measurement tasks. for tool calibration and quality control: for caliper and micrometer calibration, machining, and inspection labs.