I will put together a couple photos and exact measurements so you can do this easily. But meanwhile you will need to acquire some "White Waxed Linen Cord" as depicted in the picture at this link . . .
I found this cord in the jewelry/craft section of my local Walmart. Apparently it is also used to make necklaces, etc. It's a small spool about the size of a half-dollar. The linen cord is about 4 times thicker that normal sewing thread. I made a comparision with the original cord (broken and petrified) that was still attached in the shutter on mine, and the two cords looked exactly the same.