Drill bit guide for 12mm heatsink

I am just trying to find a drill bit that would make a decent fit for a 12mm dia copper module.

I have found 31/64 ( actually 0.4844") as being the closest drill bit to 12mm
12mm translates into 0.472"

What are you using to machine heatsinks? :thinking:

This question is aimed directly at metalworkers!

:can:
Thanks