A belt is not just a belt, just a belt. Buy from someone reputable, not the cheap stuff on that auction site where they have a zillion of them in a warehouse that are "close enough" in width/diameter/thickness made of recycled car tires.
I have a couple Dual tables, and I always stock replacement belts from Thakker (noafil), because they are "correct"--sure, I can get a dozen of them from China for 25% of the cost of a single belt, but at least they fit correctly and maintain speed correctly.