Plastic spiral balance

This is a very special balance that will have to be custom made. Before we can offer you a price quote, we need to know the length of the tube and whatever is printed on the tube. You said you couldn't find anything on the tube, though, which could be a problem. There really ought to be something there. I would check the other balance in the window, or from an identical window (if there is one). We will need that in order to identify the proper strength of this balance. They need to be very precisely calibrated so it's important. Finally, let us know how many you need.