z33/y33 drilling spindle to 14mm question

[mikey976]

i am installing y33 brakes on my s13

for those of you who have done this, what kind of drill bit is needed to drill through and widen cast iron?

i purchased a 9/16-14mm steel bit but it barely made it 1/4 of the way through.

i have read online you need a carbide bit but i am unsure and some input from those who have done this would be helpful.

thanks in advance