1720 Window channels
A handy person from Boca Raton says:
January 5, 2015
The channel is 18" long and 1/2" diam. The channel is stamped 1720
Tom from SWISCO responded:
January 7, 2015
Hey, thanks for posting. I've narrowed this down to two possible channel balance Series: either our Series 351 or our Series 390.
Now, as you can see, the only difference between these two Series is their bottom shoe. The Series 351 uses the 15-002 while the Series 390 uses the 15-001. I can't quite tell what you have based on your pictures, though. Please carefully compare their dimensions to your own hardware and see which is a better match.