Anchor discs are pressed, trued, and balanced on precision dowels. This assures that the discs will be mounted on the grinding machine accurately. Without these dowels, the normal tolerances of the mounting hole size in the steel disc wheel and the mounting screw diameter allow the abrasive discs to be mounted a little off center. This leads to "run-out" of the abrasive discs and an out of balance condition.
Precision dowels are usually located in the center of a chord, or straight line between two adjacent inserts, on the outer bolt circle. Since they are placed on a chord the dimension between dowels is usually an uneven number. For example, dowels on the ASA 30" are on a 25.996" diameter.
When reporting the precision dowels location give the diameter of each dowel and the distance between their centers. For example, the 18" ASA drilling has two separate dowel sizes and locations:
A. 1/2" & 9/16" diameter dowels are centered on the 14.028 diameter circle.
B. 1/2" & 5/8" dowels are centered on the 16.000 diameter circle.