I like to use 600 grit ( sorry I am not sure if this translates the same across the world....what is 600 grains per square inch in metric terms? ).
Grit in sand paper has nothing to do with particles per square inch (at least not directly), and 600 grains per square inch would be about the coarsest sandpaper imaginable... It would be something like a 20–40 grit!
For more on what grits mean, see http://en.wikipedia.org/wiki/ Sandpaper#Grit_sizes
The nearest equivalent of 600 paper outside of the U.S. is (P)1000 or (P)1200.
Best, Arle
