Flex wheel hole is huge

I just received flex wheels and I have noticed that the hole is huge, so I was told to jam washers into it but that seems really unstable…
how do I use them?

I guess you didn’t read the BOLD print on the page description: Flex Wheels - VEX Robotics


If you use your search bar on the fourms, you find some threads where your colleagues discuss other methods of mounting flex wheels, too.