Tungsten putty weight may be designed for pinewood derby cars, but it will work equally well for adding weight to freight cars. Put the putty between the center sills or in other tight spots to add up to 1 ounce of weight to your rolling stock.
This lead-free, non-toxic, soft and pliable, non-hardening material is easy to mold into any shape.
Brand: PineCar manufactured by Woodland