Stamp on balance

A contractor from Florida Keys says:
Not sure what one to order 24" long with these markings on it 2390 imp 26 bsi
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Tom from SWISCO responded:

I'm not sure what you have, unfortunately. We have dozens of different balances with that stamp. It's not a product code or anything, it just indicates the strength of the spring.

In order to figure out what Series this is, I need you to remove an undamaged version of this balance from the window and show me clear pictures of the top and bottom nylon fittings. I will also need to know the dimensions of these fittings.

A contractor from Florida Keys says:
More photos
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Tom from SWISCO responded:

Perfect, thanks. Based on what I see here, you have either our S380-24 or S385-24, 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.

Furthermore, since your stamp ends with "26" there is a good chance that your sash is 26 pounds. In that scenario you would want to select the 2350 stamp option, which holds 23 through 27 pounds. However this is an educated guess. You should weigh your sash before you place your order just to be 100% sure. Stamps can be wrong but the scale never lies, and it's worth it for the peace of mind.

Comparison of the S380 and S385 balance shoes.
Comparison of the S380 and S385 balance shoes.

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