Weird things in toy land

Maybe the product designers in another country who don't speak English as their first language heard that we have nuts behind the wheels here.

Possibly they were used on a track similar to hot wheels.  The weight added stability and speed.

Pretty sure Joe is right. Unless you plan to print a batch of moonshine jugs for the trunk and actually fill them, you’ll need some weight, especially if you build Bristol.  We found that out the hard way when we all abused my cousin’s slot cars. The effect is even worse than an underweight real car on a short track.
Every once in a while I wonder how long it took most of us to quit running everything at full throttle. Real cars and trains would have been generating sonic booms!

Any chance as a 'tribute car' they were originally advertised as containing a souvenir part from a real stock car, and the nut is such an item?