Herbie rates his balls according to the load they will tolerate. I think he sells at least two types that differ in differ in size and possibly elasticity, to account for variation in mass. Since his balls are relatively inexpensive and since he has made the determination of appropriate mass for each product for us, I would tend to choose his stuff, rather than some random balls from a sporting goods store or hardware store. Plus, you get the cups that keep the balls and your precious turntable from rolling around. Don't get me wrong; I am as much of a DIY anarchist as anyone, but sometimes buying the commercial product does make sense.