I think is top sash guide.

A home owner from Florida says:
December 12, 2019
Try to find replacement one. Was not sure which one I should buy.
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Bob from SWISCO responded:
December 12, 2019

Thanks for posting. Start by comparing your old top sash guide to our 18-199. Let us know if it differs in any way. 
5/8" Sash Carrier, Jordan
5/8" Sash Carrier, Jordan
18-199
$3.92
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