Precision meets reliability with the SPI Rectangle Steel Gage Block. This 4-inch Grade AS-1 gage block is an essential tool for dimensional calibration and measurement verification in machining and quality control applications. Manufactured to exacting standards by SPI, this rectangular steel block provides a reference surface with exceptional flatness and parallelism. Each block comes with NIST Certification, ensuring traceability and confirming its compliance with national measurement standards. The durable steel construction offers excellent wear resistance and dimensional stability over time, making it ideal for frequent use in industrial settings. Whether you're setting up machinery, calibrating measuring instruments, or performing quality inspections, this gage block delivers the accuracy and consistency professionals demand. Part #15-089-6 represents SPI's commitment to precision engineering and measurement excellence.