SWISCO - The Replacement Hardware Authority

I'm looking for a few of these...

A handy person from Montreal says:
Could you please help me identify the type of balance spring I need?

On it, is stamped 28C, and I think U.SB

On a more recent replacement part, it is written in ink: 11/07Unique 28-B-20.

The metallic part measures 1/2'' x 29''

User submitted photos of a window balance.
Profile picture of Tom
Tom from SWISCO responded:
Hey, thanks for posting. I've narrowed this down to two possible channel balance Series: either our Series 351 or our Series 390 balances.

Now, as you can see, there is only one difference between these two Series, and that is their bottom shoe. The Series 351 uses the 15-002 while the Series 390 uses the 15-001. I can't quite tell what you have based on your pictures, though. Please carefully compare their dimensions to your own hardware and see which is a better match.
15-001 and 15-002
A quick learner says:
Thanks for the quick reply.

It looks like the 15-001 shoe, so the 390 series. I'll order these,thanks!
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