Pitch still continues to be an issue, and has caused a lot of worry by consumers that dont want to buy the wrong thing.
Basically, if you live outside the snow belt, odds are you have a roof that has a pitch of between 4 and 8. Some older homes have pitches of 9 or 10. If you live in the snow belt or have a custom Tudor, A Frame, or some other very steep roof you have a high pitch roof and need special knowledge to walk on it. Similarly, if you live in the deep South and West, you may have a flat roof, which is self explaining.
So dont worry about roof pitch when ordering. The S model will fit most roofs that are angled, and the F model fits the flatter roofs.