Unable to identify spiral balance

A contractor from Raleigh, NC says:
I can't find any manufacturer information on this window; no bar codes or stamped ID. Please see the attached pictures. The balance is 22" long. It appears to have 'snapped' at the spring from within the balance casing. Thank you in advance. BTW - This is how it came out of the window frame, i.e., there are no missing parts.

User submitted photos of a window part.
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Tom from SWISCO responded:
Thanks for posting! Before I can offer an applicable replacement for this balance, can you give me the length and diameter of the plastic tube? Can you also give me the weight of the window sash?
A contractor says:
The length of the tube is 20 7/8" and the diameter is 1/2". I don't have immediate access to the frame, so I could only guesstimate the weight. It's a double-hung window approxiately 48" wide with double-pane glass. Using the weight of a similar size item (3/4" plywood), I would suggest the lower sash weighs 20 lbs.
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Tom from SWISCO responded:
Thanks for posting! We actually don't have any spiral balances whose diameter measures an even 1/2". It sounds like you may have either our Series 600 spiral balance, which has a 5/8" diameter, or our Series 900 spiral balance, whose diameter is 3/8". Which of these do you think are closer? I would also recommend that you go with a 21" length.

Now, we have a few tip options for our S600-21 and our S900-21, and each can support a different weight window sash. I will relate them here for you to compare to your own window sash weight.

Red Tip: 6 through 19 pounds.
Blue Tip: 10 through 29 pounds.
Black Tip: 30 through 40 pounds.

Red Tip: 8 through 21 pounds.
Blue Tip: 21 through 22 pounds.

Please keep in mind that the weight range information is based on 2 balances per sash. Balances are designed assuming friction in the jamb weather-strip will carry a portion of the sash weight. Suggested sash weights are approximate.

Let me know if you have any questions!
A contractor says:
I measured it with a micrometer: OD of the tube is .500 and the spring is .425 (see attached pic - I cut it open).
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Paul from SWISCO responded:
Thanks for getting back to us. I think that our larger diameter Series 600 spiral balance would be closer.
A contractor says:
Thanks - I went with the S600-21 in a Blue Tip.
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