It's time to add a new, versatile tool to your knitting: circular needles. What makes them different from straight needles or double-pointed needles? Circular needles have pointed tips and come attached with a length of smooth nylon or plastic cord. Because circular needles allow the weight of the work to rest in your lap (rather than on the needles) they put less strain on the hands, wrists, and shoulders. (This is especially helpful when you're working on heavyweight garments like sweaters, vests, and chunky-style cardigans.) If you like to knit while traveling—a commute on the train or a trip by flight—they're convenient because they eliminate the risk of dropping a needle mid-transit.
You have two common techniques when knitting on circular needles: join the work to make tubular pieces or work each row back and forth to make rectangular pieces. While they are most intended for knitting in the round, you can easily adapt circular needles for flat knitting by turning your work at the end of each row. The benefit of using circular needles for flat knitting is that it distributes the weight of your knit piece, especially when you're working with a high number of stitches.
Circular needles come with sharp pointed tips (for detail-oriented lace knitting) up to rounded tips (for bulky-style projects). The needle cables can range from 9 inches up to more than 40 inches. Interchangeable needles can be attached and detached from a set of cables, allowing you to customize knitting to practically any size and length. These should attach firmly to the cord without unscrewing and coming loose. Many sets of interchangeable needles have connectors so that you can further extend the length of your knitting for items like bed-size blankets. Just remember that the length of your circular needles should be smaller than the diameter of the tube you are knitting. Otherwise, the stitches will stretch as you knit.
When choosing circular needles, pay close attention to the join—this is the area where the needle shafts meet the cord. A roughness here can cause stitches to snag, slow down your knitting, and shred your yarn. A cord should be strong enough to support the weight of your knit piece while flexible enough to allow your stitches to move smoothly without kinks. (Here's a Good Thing: If the cable on your needles becomes coiled too tightly, try soaking it in warm water to relax the kinks.) Some circular needles swivel at the join, which eliminates this problem altogether.
How to Knit with Circular Needles
Cast on the stitches, distributing them evenly. The last cast-on stitch is the last stitch of the round. Place a marker here to indicate the end of the round. In doing this, be sure to keep your stitches even and do not twist them. If the stitches become twisted, the knit fabric will become twisted and once you've completed the first round, you will have to undo all of your work to straighten them. Work until you reach the marker again; this completes the first round. Slip the marker to the right needle and work the next round.
Some prefer to knit smaller pieces with two circular needles as an alternative to double-pointed needles. In this method, you cast on the number of stitches as required by your project and slip half of them to the second needle, then slide the stitches to the opposite ends of your needles and join to begin knitting in the round.
Magic Loop is a technique for knitting in the round that avoids the use of double-pointed needles. Using longer-than-average circular needles, you can knit smaller items like socks, sleeves, and mittens. This method is usually done with a circular needle cable that is 29 inches or longer, although the ideal needle should measure up to four times the size of your project. You can even knit a pair of socks or sleeves at the same time. (Hence, the "magic.")