The Model B- 75 Tester was developed to obtain more sensitive response to slight changes in the upper range of hardness covered by the Model B. This sensitivity is particularly useful in testing mild steel and the stronger aluminum alloys. For brass the B-75 covers the range from annealed to full-hard. This added sensitivity is accomplished by incorporating a penetrator of slightly different contour and a heavier load spring than used in the Model B. The 20 graduations on the Webster dial indicator covers the range between 20 and 100 on the Rockwell B Scale.
The graphs on this page show the range covered by the Model B-75 Tester. Results were derived from many samples, and show the average curve. All tests were conducted with the Model B-75 Tester set to read 5 on a standard test strip of 6061-T6 aluminum alloy of Rockwell E 90± 1 hardness.