What size holes do I drill in my hubs for 6 lug conversion?

[Brettm57]

I'm fixing the brakes on my '88 hatch right now and I'm thinking that as long as I have the hubs apart I might as well drill the holes in the hubs for a six lug conversion. I don't have rims yet, but plan to some day. If I drill them now though that will save me tearing the hubs apart again later. What I need to know is what size drill bit to use. I'm guessing it's metric, which I don't have, but I'll go buy the size I need. For what it's worth, I have access to a vertical mill, which is how I intend to drill them. Thanks.