They are G5's brand of "custom" strings. Metrao is the proper spelling.

Elite now uses them (albeit supposedly beefed up a little), I had mine on the GT-500 and I think it's a very good string. It reminds me of a Stone Mountain string- a little more movement at first than say a WC or other custom maker, but settles fairly quickly and then locks down.

http://www.g5outdoors.com/metrao/metrao.php