the part connects the bottm of the spiral rod to the pin in the window

The part in question is called a pivot shoe. Yours in particular is an older style that isn't made anymore, but I believe you can use our 15-046 as an alternative. Just make sure to review our dimensions before you buy anything. Please also note that will need to take the old shoe out of the window if you want to get accurate measurements; you can't do that while it's still in the track.

Alternate image for 15-046