Coil Balance Pella Window

A handy person from Hatboro, PA says:
This coil balance is in my son's single hung Pella window. It's a double pane window and it's near impossible to read the Pella serial number between the two panes of glass. I also can't seem to find anything online that looks exactly like this. The only number I see is the 10 that appears clearly on the front of the plastic piece in the photo. I know you ask for photos installed and removed but that's the other problem - I can't figure out how that assembly comes out of the channel. I've tried prying with a screwdriver but I don't want to destroy anything and it's not coming out with a goof bit of force applied. Hopefully you can see that there are actually two coils - one in the plastic part and one that is exposed and sits above the plastic part.
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Bob from SWISCO responded:

Greetings. I believe this is either our 15-251 Single Coil Support, or the 15-252 Dual Coil Support. It depends on how many coils each side of the window used, and while it appears to be two, its very possible the single coil unspooled when it broke, to give the appearance of two. 

This balance system uses our Series 160 Coil Balances. It may be best to weigh the window sash. Give me that exact weight, and I can tell you what spring weights you need. 

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