August 27, 2015
I bought my house in 1968. It has spiral balances in one window, dating to 1966. The windows measure 52" W x 26" H
The bottom sash moves up and down on plastic spiral 23" long, 3/8" wide.
About 1/4" from the end, at the top, is a rivet to hold the balance to the jamb.
It looks exactly like your series 300, but I can't see the red tip. The shoe and everything else looks like your 300, but my shoe is aluminum.
I can't figure out how to remove the spiral piece that is connected to the aluminum shoe. The shoe will slide from the very bottom of the window to the top, in a track that has a capture. BUt I don't see any way to take it out.
The balances have not worked for the past several years. It's time to replace them.
September 1, 2015
Here are pictures. the sash weight is 15-1/2#
