https://www.crossco.com/services/calibration/dimensional/gage-block-calibration/
Gage block calibration equipment and services provided by Cross Precision Measurement. On-site or in-lab calibration for gage blocks from a trusted metrology...
gage blockcalibrationservicesprecisetolerances
https://www.nist.gov/publications/gage-block-handbook
Gage blocks are the primary method used by industry to standardize the measurement of dimension.
gage blockhandbooknist