I would estimate 500 each, but you can do better by pulling one slide right out and reading the label on the very first wrap. Take a close up picture with your camera of the label, and then look up the replacement.
I did a 6 foot unit by myself. You really need two people on two tall ladders or alongside a wall or platform (best option) as once you start to put it in, you can't stop. Study the U-tube videos to see how to do it.
Lot's of spring pressure there, but OK if done properly. I also replaced a garage door spring in my house.
