Step drill bits (where to get) ?

[birchy]

That's a countersink not a counterbore? Big difference between the two. I also had a quick search for counterbores with a combined pilot drill so that you could effectively drill and counterbore without changing tools but came up blank. I've worked in engineering for many years but have never seen such a tool. Or at least not a proper one. I guess you'd have to get a lump of tool steel and make your own or make one by grinding a suitably sized drill bit.