That's the window channel, and it looks like it has lost all the fabric covering (pretty typical) and needs to be replaced. That's what you'll be purchasing. Be sure to save the clips (one can be seen on the right of your photo.


Kevin
1951 Chevy 3100 work truck
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Photos
1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.