There are many sizes and if you look at many power cords some look like a snake that just ate a mouse and that is usually the ferrite bead.
If yiu have old cords they can be cut out.
Larger ones will allow a small wire to be wrapped through and smaller ones not so much.
These form a choke that blocks high frequencies in the wire.
Small beads can be slipped over single wire connections at terminal strip to block things from terminal strip to wire
Tony & Lori
1989 Country Coach Savannah SE