Quote Originally Posted by gwernaffield View Post
....... Delrin is used for making all kinds of stuff including gears also delrin balls are grade one the highest grade you can get for roundness and smoothness, the ceramic balls are grade 5 , the steel balls are normaly grade 10 , unless it is aspecial order and 4 times the cost of grade 10 .......
Just need to make a slight correction here, Delrin balls are graded in thousandths of an inch, so a grade 1 ball is round to within 1 thou, which is approximately 25 microns. Ceramic balls, certainly silicon nitride ones, are graded in microns so a grade 3 ball is round within 3 microns.