What Die Grinder bit to use? Need to enlarge antenna hole in fender

Tape over the hole and top fender surface with a couple layers of 3m painters tape and use your template and mark it out with a fine tip sharpie.
next use a sanding mandrel to enlarge the hole then use a small carbide bur for the two small open slots. Be careful with the carbide bur when you get them in tight spots they have a tendency to grab the other side of the hole or slot and get uncontrollable. I did this very job on a 68 barracuda fender to allow a 67’ antenna to fit.