Channel guides.

Hello! Sounds like you're talking about the bottom balance fittings. The one in your photos is the bottom shoe, either the 15-001 or 15-002 depending on depth. Review their specs to see which one is a closer match.

You also mention a top fitting but I don't see it in your photos. There are a ton of different possibilities so I need to see it before I can make a recommendation.

It is possible to replace these fittings and reuse the balance and I'll share instructions on how you may do so below. However, keep in mind that when these fittings break, the balance is usually not far behind. In all likelihood you will have to replace the whole thing.

If the string has popped then replacing the top and bottom fittings alone won't solve the problem. You need all new balances.

Based on these new photos I think there's a good chance you have our S395-28. This comes with a 19-005 top fitting and 15-001 bottom fitting pre-attached, but you should review both of these pieces to ensure they're the same as what you have now. I think they will be, but it never hurts to check.

Yes, that's 100% correct. You only measure the metal channel. Based on your stamp it should be 28" long.