https://reddit.com/r/typewriters/comments/1p42tr1/typewriter_ribbon/
It's a small metal ring/hub that fits onto the ribbon spindle. You can call around to repair shops for replacements (which may be the cheapest route) https://site.xavier.edu/polt/typewriters/tw-repair.html. Ribbons Unlimited https://ribbonsunlimited.com also sells these hubs with ribbon attached, but it's more expensive to do this, but once you've got them, you can buy ribbon by itself for much cheaper in the future and just wind the new ribbon onto existing spool hubs.
Here's some useful videos which might help you out: - https://www.youtube.com/watch?v=iTFM54VKKc4 - https://www.youtube.com/watch?v=xWQTa4b7jPs (This one has some advice about using a Remington without the spools.)