ABR-1 ?
The ABR-1 is the original name of the Tuneomatic bridge used on Gibsons. An original ABR-1 will have 'ABR-1' cast into the bottom of the bridge. Later Tuneomatics will have a patent number cast into it. The early ABR-1 bridges did not have the retaining wire for the bridge saddles, though later on they did. Also, ABR-1 bridges used plated brass saddles, later ones were made from a different type of alloy.