What’s the difference between these two models? I can find nothing on the web. Are the bore sizes different?

King used "Silvertone" to describe a sterling silver bell until they lost a trademark suit with Sears (who made a student grade trombone called Silvertone). King models after the trademark loss are called SilverSonic. There is no difference between a 2B Silvertone and a 2B Silversonic except that the Silversonic is newer. You will never find a 3B, 4B, or 5B Silvertone as these models were introduced after the trademark lawsuit.

[quote="BGuttman"]King used "Silvertone" to describe a sterling silver bell until they lost a trademark suit with Sears (who made a student grade trombone called Silvertone). King models after the trademark loss are called SilverSonic. There is no difference between a 2B Silvertone and a 2B Silversonic except that the Silversonic is newer. You will never find a 3B, 4B, or 5B Silvertone as these models were introduced after the trademark lawsuit.[/quote]
You will find silver-belled Symphony models (pre-5B) with the Silvertone name on them.