'Been doing some gun bluing lately...thought I'd share some Google searching:
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I always thought that 0000 steel wool was finer than 400 grit - guess not.
No wonder I had to go back and hit it with 1200 grit.
4/0 steel wool = 400 grit sandpaper
3/0 steel wool = 280 grit
2/0 steel wool = 180 grit
2/0 steel wool = 120 grit
1 steel wool = 100 grit
2 steel wool = 60 grit
3 steel wool = 50 grit
4 steel wool = 36 grit
Anticipating the next question:
White Scotchbrite = 1200 grit (it has no abrasive)
Gray Scotchbrite = about 400 - 600
Maroon Scotchbrite = about 220-280
Green Scotchbrite = about 150 - 180
Be a little careful. Different manufacturers of non-woven abrasive material may be somewhat different.
The above is for 3M Scotch-Brite brand.