I modeled this for a 3Derby at my school. It includes a small container for the little weights and a spot for a M12 bolt to increase weight. I used an actual bolt and washer but have included a 3D printable version if you want it to have a fake bolt.

The only part that needs glue is the screw holder otherwise you will need to used a clamp to attach the axles. I have included a .3mf for bambu printers if you want all the multicolor of the clamps. I would include more pictures but I left my car at school and will have to wait a week.

Let me know if I missed any files or if you want any part modified for your needs.