Sandpaper grit chart

I never realized that there were two different scales. This came from Woodworking magazine

" Coated abrasives (the technical name for sandpaper) follow one of two common grading systems used in North America: CAMI (Coated Abrasives Manufacturers Institute) and FEPA (Federation of European Producers of Abrasives).
FEPA products are sometimes called "P grade" because that letter prefixes the grit number on the back of the sandpaper, as shown at right. If there's no prefix, you can assume that it's a CAMI-graded product. As you can see in the chart at right, particle sizes in the two systems closely paral-lel each other up to about 220 grit; then FEPA numbers increase rapidly. If there is a letter after the number, it refers to the weight of the paper or fabric.
Manufacturers may use one or both systems for various lines of abrasives. For example, Klingspor uses the FEPA scale exclusively, while 3M uses both scales.
A second key difference is that the CAMI standards permit greater variation in particle sizes used within each grade. That may the texture difference you noticed.
"

Hope this helps someone else

Bob