Identifying channel balances

I'm hoping to buy 20 channel balances to refresh my home's windows. The photos I took of the ends may look strange; I believe tiny parts of plastic have worn down and broken over time.

Additional info:
- The only stamping on my channel balances reads "27 4 BSI OD" (BSI text is stamped perpendicularly to other text).
- The metal portion of the channel balance is 28 inches long.

Thanks for your time!

Thank you for the speedy and thorough response, Jasmine. I'll go with the S380-28 since the shoe on my channel balance is 1".