I just ordered 2 new attys, i got a replacement 510 for a friend and a boge 2.5 510. I cant tell the difference between the two. They both look almost exactly the same. One is just slightly more matte in color, and the one that is shinier has a tad bit wider bridge. I am thinking that the one with the slightly wider bridge is a 2.5 but i think its going to be hard to tell with the ohm difference so little.