Metal screws

[richsc]

When I was visiting colonial Williamsburg this weekend, the blacksmith docent mentioned that metal screws were known to the Romans, and that he had read of that. I know of only one metal screw example in a Pompeii bronze trivet that screwed together, rather like some cheap Walmart furniture. But I have not heard where the Romans might have used metal screws or seen any examples. Anyone know of any examples out there, and if so, how they would have made them?