QUANTITY: 6 x Tungsten Ballast Cylinder shaped pieces 6.3 A~ x 1 mm x 6 x 0.58g = 3.5grams.
NOTE: Non Lead Ballast - 70 % Heavier than Lead
Until recently lead was the material commonly used to weigh and balance the slot models. The toxicity of this metal is now out of the question - unfortunately, however, the dose considered critical has been significantly lowered, especially for children. It's a substance, in short, that is really really bad for your health.
So, how to replace lead? Plutonium and uranium, with their very high specific gravity, would be
ideal but are a bit dangerous ... and hard to find.
Gold would be perfect: dense, non-toxic, if it only wasn't so expensive ....
The Slot.it Tungsten ballast answer all three questions: non-toxic, weights as much as uranium, and does not cost as dear as gold.