This type of fold has two limbs of equal steepness. It results when the two opposing forces moving towards each other are of equal strength.
This fold has one limb steeper than the other. It results when one opposing force is greater than the other.
This fold has one limb pushed over the other limb, until the axis of fold is almost horizontal and the two limbs are almost parallel. This is formed when one opposing force is very much greater than the other.