Felting needles are the most important tool for needle felting. They are specially designed with notches or 'barbs' all along the shaft to mat and lock wool fibers together. They come in a variety of sizes: smaller needles have finer barbs and can be used for more detailed work, while larger needles have thick barbs and can create felt faster than other needle sizes. The needle size is measured in gauges ranging from 12 to 42. It is a measurement of how many needles fit in a square inch. That means the higher the gauge, the smaller the needle.