"Rivets" said the tour guide. I was at Titanica, the exhibit of the lost liner's artifacts, and standing next to a two-ton piece of the liner that had been retrieved from the Atlantic's bottom. It was awesome looking at that old, sunken ship -- and admiring its massive construction. I also looked at the holes where rivits had been "zipped" out during the liner's submersion. I am also now reading a new book on the metalurgy involved in the Titanic's hull plates and the rivits used to hold the hull plates together.Fascinating.