A. Grade 0, Webber A1: The most popular grade of blocks:
1) it is accurate enough to perform 95% or more of all applications. This grade is recommended for general
2) most steel blocks are Grade 0, and steel is the most popular choice of gage block materials.
Most gage blocks are used to check micrometers and calipers. Assuming a micrometer needs to be calibrated
to an accuracy of .0001". If the 4:1 accuracy ratio rule would apply, then grade 0 gage blocks must have a
tolerance of not less than ±.000025µin. In fact, the tolerance (up through 1 inch) is ±.000005. Thus, in this
application, grade 0 gage blocks are 5 times more accurate than needed.
B. Grade 00, Webber AA: These blocks are to be used as laboratory references or to calibrate gage blocks
with lower accuracy grades. It would be very unusual to use grade 00 blocks on the shop floor. The accuracy
of measurement is only slightly improved over grade 0 tolerances, but at a much higher cost. This additional
cost is usually only justified when reducing measurement uncertainties is absolutely required. Available from
Webber in the croblox® or ceramic materials. Not available in steel.