Heavy hubs.. I have used them before. They will usually fit in the spinner if you are using one. There is now another similar product, Heavy backplates. 1 oz., 1.5oz, and 2oz sizes available. The great thing about these products is that they are weight that is applied as far forward as possible. That means you will need the least ballast thats possible. And yes, they do act as a fly wheel to steady the idle! They are not going to come loose. And you can make adjustments by simply changing one for another. I love them.