Gravel for Tyco US-1 Trucking Slot Car Set

This is some replacement gravel I made for my old Tyco US-1 Trucking Slot Car set.  I don't have any original gravel left, but remembered I could use BB's as a substitute back in the day, but they are a bit too heavy.  So I made the plastic gravel about the same size.  

They are 4.5mm spheres, with 0.4mm cut off the bottom to create a flat spot so they would be stable and stick on the print bed. 

I printed with PLA at .20mm layer height in Quality mode.