Sash mechanism housing

A contractor from Minneapolis says:
27hd mr

Not sure what part I need to replace. Window won't stay open.
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Bob from SWISCO responded:

Thanks for writing in. Looks like you need a ribbed channel balance for a tilt window. See our standard selection here. You will need to remove the balance from the window to confirm what kind you have. You will need the length of the metal channel, and you'll need to identify any end attachments on either side of the balance. I think it's possible you might have an S751-28 with a stamp option of 27HD. But it's best to confirm this. Send us pictures of the balance out of the window if you are uncertain. 

How to install a ribbed tilt channel balance with knife lock shoe
How to install a ribbed tilt channel balance with knife lock shoe
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