Identify this balance please

A home owner from St Pete Beach, FL says:
The window say EFCO ANSI Z97.1-1984
The metal part measures 27 inch's long and 5/8 inch wide.
There is a stamp with 2616 (in picture) back side of extrusion.
thank you for your help
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Tom from SWISCO responded:

Thanks for your photos. Based on what I see here, you have either our S351-27 or S390-27, depending on the depth of the bottom shoe. That's the only difference between them. I recommend measuring your shoe and referring to our dimensions to confirm the best match.

As for the stamp, yours is very peculiar. I don't believe 2616 is something I've ever seen on this series before. Please give us a little time to look into that and I'll get back to you ASAP. For now, please just verify which of those two Series you have so that we have that information in hand when we need it.

Comparison of the S351 and S390 balance shoes.
Comparison of the S351 and S390 balance shoes.

A home owner from St Pete Beach, FL says:
the shoe is 1 1/8 inch so the S390.
thank you for your help
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Tom from SWISCO responded:

Thanks again for your patience. I'm sorry to say that we weren't able to find a record of what that 2616 stamp might represent. It really is a weird one.

With that in mind, would it be possible for you to get the exact weight of your sash? The plan now is to basically start from scratch and figure out how these springs need to be calibrated. Ideally our S390-27 has a standard stamp option that can match that weight and do the job for you. Knowing your exact sash weight will let me verify.

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