Knitting needles are the primary tools of the knitter. They come in a variety of shapes, sizes, colors, and materials, and an avid knitter will often collect quite a large set of needles. One of the key properties of knitting needles is the Needle size. The size of a knitting needle is measured by the diameter of the shaft, and this value determines the size of the stitches created with those needles, thus playing a key role in determining Gauge.