The best mounting size is for a 12mm screw, but it's tricky.
Optimal size for a 12mm screw, but hard to find locally. Drilled new holes in the spindles to accommodate a larger brake with other factory parts. Took 4 holes through 2" of metal, still looks sharp but probably won't need it anymore.
Pros
Black oxide coating cools and lubricates drill bit for longer tool life.