Dec 12, 2008· Posted December 11, 2008. I use 963G 3M belts for rough grinding in 50, 80, and 120 grits, and then switch to 303D 3M belts for finer grits. If I need really fine grit belts for handle work I like the Knlingspor Jflex, but I can't remember the number. I work only simple carbon and low alloy steels either plain or in pattern welded.