Felting needles come in many different sizes. Barbs lock the wool fibers in place. Smaller needles have finer barbs and can be used for more detailed work. 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.