I'm assuming you mean 830, not 820. The 830 bobbins have metal on one side that the machine reads. These bobbins need to be stored so the metal isn't scratched and worn off. The donut shapped bobbin holders are made in a larger size to fit the 830 bobbins. The Fresno, ca Bernina dealer, Sierra Fiber Arts, carries them.
My 830 came with a plastic box that fits them. I think I'll cut disks of cotton batting to fit between them.