You know, it all depends on what you are working on. I have done some stuff where a 60 grit disc would be used last to remove tiny imperfections back in my day as a the lead welder in a local machine shop. 100 to 120 grit for really polishing things! Stuff that was several inches thick and needed a 20 ton crane to lift and move !!It was fun when I was young, just what I wanted to be doing!! I think some of it would kill me now!! But I would do it all again if given the chance.
Type at you later,
Dan McEntee