Interchangeable Knitting Needles allow you to create multiple size and length circular knitting needles by interchanging the parts. You can buy individual interchangeable needles and cords or you can purchase them as a set with multiple cord lengths and multiple needle sizes that you can mix and match for the exact size circular knitting needle you need. This saves you money because you can buy one set verses having to purchase multiple circular knitting needles in every size and then also in every length. Interchangeable knitting needles have become very popular for this reason. It saves you from having to buy so many individual circular knitting needles.