I either don’t get what you’re saying or didn’t explain the brake cable structure of the bike well enough. It looks like this:

brake lever—housed cable—transition to unhoused via cable stop—unhoused cable—transition to housed via another cable stop—brake itself, more transitions there but that doesn’t matter here

At each transition between housed and unhoused, I need one of these pieces (or something similar), but since I lost one of them, I only have one.

But as the other replies all suggested full housing instead of bothering with this ferrule thing, I think I’ll just try that.

It’s a no-name bike from the 2000s, Wheeler Pro 39. Thanks for your input, I’ll try full housing first as that seems the most straightforward.

Thank you, I’ll do just that and see how I fare with full housing 👍