3M Micron belt question

[Cloyde]

OK Grit I understand but Microns are somewhat confusing, Principal I understand but my question is I have ordered 3m micron belts 60,40, 30, 15 and 9. My pops supply cataloge has them listed as 60= 240 grit, 40= 360, 30= 600, 15= 1,000 and 9 = 2000 grit. Jantz supply has the same belts listed as 60= 220, 30= 400, 15= 600 and 9= 900. can someone tell me what is correct or are they all wrong? I have looked at other sites and have not found them listed as compaired to grit only in micron.
Thanks to anyone that can help there is a big difference.
Cloyde

 

[Stacy E. Apelt - Bladesmith]

Grit to micron conversion varies a lot. Some charts are based on the average particle size (which varies a lot).Others are based on the smallest or largest particle size.

This chart is not the final word, by all means, but gives a lot of good info on abrasive comparison:
http://users.ameritech.net/knives/grits.htm

Notice that, depending on the maker, some are finer rated than others.
Stacy

 

[TekSec]

1. 3M I.D. Number: 372L
2. Mineral: Aluminum Oxide
Grade Approximate Comparison Print Total Thickness Average

(micron) ANSI FEPA Color (units = mils)
9 1200 P2000 lt. Blue 8.0
15 600 P1200 orange 9.0
20 500 P1000 red 9.0
30 400 P500 green 10.0
40 320 P400 blue 11.0
50 240 P320 purple 12.0
60 220 P240 black 13.0
80 180 P180 black 16.0
100 150 P150 black 19.0

 

[Cloyde]

Thank you for the help, and taking the time. I was unsure and could not fined anything that helped on the net.