This gauge of reverse is good for needle felting the heavier wools such as British or Scandanavian types.
Standard felting needles have tiny barbs along the length of the shaft. The reverse needles work in just the same way, except the barbs are facing the opposite direction. This means that the fibres are pulled outwards. The results are the same, but leaves a slightly fuzzy layer on the outside of the piece. This is a wonderful effect on its own, but it can also be useful if you intend to finish the piece by wet felting the outside.