I want to replace windows psrt

A quick learner says:
Please help me to identify this part. I see 2830 and the hight without plactic part is 28 3/4", which I think consider 29". Both plastic pieces on the top and bottom have wings. The closes I found is S380 2830.
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Casey from SWISCO responded:

Take a look at our S371-29 channel balance with a 2830 spring strength option and see how it compares to yours. Thanks for posting! 

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