What spiral balance do I need?

A quick learner from USA says:
Looking for a spiral balance for a tilt window.my old balance has a vinyl sleeve that has a diameter of 5/8 but the metal rod underneath measures 7/16 my guess would be to order the 5/8 size with blue tip which is the color I currently have also the rod seems to measure 28and1/2 not including blue tip would like your help answering a few of these questions thanks
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Tom from SWISCO responded:
Thanks for posting! Yes, some old balances used plastic outer tubes instead of our metal. We prefer metal since there's less of a chance for them to break or shatter, as plastic tubes are prone to do.

I'm not sure about the length. Is that the length of the outer tube alone? If so, tell me the height of your visible glass for the sash this balance supports. That will help us calculate the length.
A quick learner says:
The outer sleeve was plastic and as you mentioned broke off when I took the balance off the window.Here is a couple pics of balance.the visible glass measures 27 inches
User submitted photos of a window balance.
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Tom from SWISCO responded:
It's so hard to be sure with just a tape measurer held next to the part. It seems to be closer to 29" than 28", though. It's definitely more than 28-1/2". I think you might be able to get away with 29".
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