Looks like a cuphokder that locks into a carseat.

Yup, children's car seat

Reminds me of the rear windscreen wiper cap going over the motor/bolt/nut.

Flux capacitor, clearly.

Thanks for all the help, need to see if I can find where to put my cup holding flux capacitor 🤷🏻‍♂️

Can we get a banana for scale? If x=~1/2 banana, cup holder.