window balance slide

A quick learner says:
I'm struggling to identify the proper slide.

it is 23" overall length. pictures the spring fell out and the strings and pullys moved out but I have close ups of the two ends and the only identifiable marking (21 4).

User submitted photos of a window balance.
Profile picture of Tom
Tom from SWISCO responded:
Please see our S385-22 channel balance, I believe this could be the balance you need.
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