Spiral balance for identification/replacement

A home owner from Wilton CT says:

Please help me identify the spiral balance shown in the attached 4 pictures. I spoke to Jody on Friday about this and she requested pictures, so here they are. The balance is from a wooden single-glazed sash, 26" wide x 20 high, vintage about 1953, manufacturer not known. I have 2 of these, plus 5 larger windows, all double-hung and in need of attention. At least one unit appears to have a broken spring. The spiral sleeve is approximately 3/8 to 7/16 diameter and 17.5" long

Details of both ends are shown. Adjustment appears to be made using a 3/32" Allen wrench on the adjustment(upper) end. The square shank with the hexagonal recess is 0.194" (5 mm) across the flats. The spring can be depressed using the Allen wrench, torsion adjusted, and apparently engages (somewhat unreliably) a square opening in the bracket when released in order to maintain the preloaded torsion. The non-adjustable end has a 1/4" diameter shank which sits it a round hole in the lower bracket I can't really see into the pockets to see whether there is a split metal sleeve surrounding this device, or if it just bears directly on the side of the jamb.

Any help you can offer to help with identification and possible repairs and/or replacements will be greatly appreciated. Thanks,

Bill 

(Home Owner, Handy Person, and Quick Learner, to use your menu of self-definitions)

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Tom from SWISCO responded:

Thanks for posting, Bill! This is definitely an older type of balance. I don't personally recognize it, but we may be able to find something. Please give us a little time to research it, and one of our balance experts will get back to you soon with a suggestion. 

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Paul from SWISCO responded:

Hey, Bill! I actually do recognize this. Like Tom said, it's very old. This specific style isn't made anymore, but we think you can use our 5/8" diameter S500-18 non-tilt spiral balance as a replacement. We've used this balance system to replace hardware like yours since the forties. I also recommend a bottom bracket like our 17-012 . Let me know if you have any questions.

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