channel balance Identification

A quick learner from Sedalia MO says:
The aluminum channel is 28" end to end excluding plastic pieces. There is a label on the aluminum channel 2730 BSI ET as shown in one of the pictures. The pictures are from an operational unit. There are two single hung non tilt windows in addition to the one the pictures were made from. Each window has a channel balance on either side of the window. The channel balances fell out of in pieces the springs are broken and the channel balance shoe or bottom was shattered on each one. The only difference between the broken ones and the the good ones is the label on the aluminum channel. The broken ones are labeled 27 C. The channel widths are 9/16". I believe they are S390 or S351 the depth seems to be more than 1" but not quit 1 1/8". Could you please give me your recommendation.
Thumbnail of the uploaded file named 20211008_183128.jpg
Thumbnail of the uploaded file named 20211008_183138.jpg
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Casey from SWISCO responded:

Hello,

It looks like you have either our S351-28, with a 15-002 bottom attachment, or S390-28, with a 15-001 bottom attachment. Take a look at the image below to determine which balance you'll need. If your attachment measurings more than 1" deep, you most likely need the S390 since these fittings can wear down a bit over time from rubbing on the window jamb when the window is raised and lowered. 

You'll also need a 2730 spring strength option for your replacement balances. Thank you!


Comparison of the S351 and S390 balance shoes.
Comparison of the S351 and S390 balance shoes.
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