Your first ever pair of blades were more than likely to be parallel sided. It is found on a variety of begginner to intermediate level blades and simply means the blades thickness is the same from toe pick to tail.
Edea Rotation /Balance
Mark 4 and Mirage
Legacy 7 & 8
Parallel sides blades have a hollow the same shape as the diagram above (on the right). The blades are easy to maintain, shapren and provide a secure grip for beginners.
Many beginner to intermediate blades are Parallel sided. They are a cost effective design to manufacture and can be an addition to a boot and blade set. They also come in a range of thickness from 3.8mm-4.2mm
Parabolic is additional feature that can be added onto a traditional parallel blade giving the blade a thinner section in the middle. This then helps the blade to reduce friction and therefore glide for longer.