Thermal Effects on Gage Blocks NIST has two sets of master long steel gage blocks. The CTE for each block was measured, giving the results in the table. There are two things to notice. First, Even though the blocks are from the same manufacturer, the CTE can be different from block to block by more than a few percent. Thus, even for gage blocks you cannot be sure of the CTE by better than a few percent unless the block is measured. Second, the CTE gets smaller as the block gets longer. These blocks are made from AISI 52100 steel, and the ends are hardened. It turns out that the CTE for the hardened steel is about 12 ppm/°C and unhardened is about 10.5 ppm/°C. Only the first few centimeters on each end are hardened, so as the block gets longer the percentage of hardened length decreases. | Length (inch) | GB-1 CTE (ppm/°C) | GB-2 CTE (ppm/°C) | Range | Deviation from 11.5 ppm/°C | | 1 | 11.90 | 11.63 | 0.27 | 0.27 | | 2 | 11.78 | 11.69 | 0.09 | 0.23 | | 3 | 12.00 | 11.74 | 0.26 | 0.37 | | 4 | 12.00 | 11.63 | 0.38 | 0.31 | | 5 | 11.40 | 11.27 | 0.13 | -0.16 | | 6 | 11.25 | 11.23 | 0.08 | -0.20 | | 7 | 11.06 | 11.36 | 0.30 | -0.29 | | 8 | 11.22 | 10.92 | 0.30 | -0.43 | | 10 | 10.84 | 10.64 | 0.20 | -0.76 | | 12 | 10.71 | 10.64 | 0.07 | -0.82 | | 16 | 10.80 | 10.58 | 0.22 | -0.81 | | 20 | 10.64 | 10.77 | 0.13 | -0.80 | | 
