Question

difference between plain dividing head and universel dividing head

Answer 1

Universal Dividing heads: some manual indexing heads are equipped with a power drive provision. This allows the rotation of the dividing head to be connected to the table feed of the milling machine instead of using a hand crank. A set of change gears is provided to select the ratio between the table feed and rotation.
dividing plate facing the user, the nose of the spindle can be either to the left of the dividing head or to its right. This is significant is when a universal dividing head is driven by the leadscrew on the milling table.