Not even feeler gauges, just a great set of nut files slighty larger than your strings. Uo-Chikyu ones are sold by japarts.ca in any gauge you want and they are as high quality as I've found. Somebody on the internet took close up photos of how a bunch of different nut files cut and they came out the best, I bought some, and can't say enough about them. Now I have everything from an .011 down to a .125 low bass string. Take care of them and they'll a typical guitarist a lifetime, and once you learn how to do it correctly and get the feel for it you're set forever.