This. Technically the radii can't even have a normal distribution, because the support of the normal is (-Inf, Inf) but the radii are bounded below by 0. So yo

This. Technically the radii can't even have a normal distribution, because the support of the normal is (-Inf, Inf) but the radii are bounded below by 0. So you might say that the radii = r + e, where r is constant and e is normal around 0 with variance way, way smaller than r. But then the volume of the ball bearings = K * (r+e)^3, and because r >> e, the largest source of randomness term is going to be 3Kr^2e, which makes the whole thing look pretty normal.