A circular needle is essentially two short needle tips joined by a cable or filament. Circular needle tips are generally about 5 to 6 inches long and range from somewhat flexible to completely rigid. Tip length is usually much shorter in shorter needles. Tips can be made of anything of which straight needles are made, although I have never seen bamboo circulars in the very small sizes, or wooden circulars at all.
The tips are joined by a strong, flexible nylon filament which allows the needle to smoothly form a closed loop. The length of the needle is generally the combined length of filament and tips, although some needles may be up to an inch longer than their stated length.
Circulars come in lengths as short as 8 inches (by the Clover company, and not very common) and up to 40 inches. Longer needles are made by at least the Addi company, but I have never seen them or heard of anyone using them. The most common lengths are 16, 24, 29, 32, and 36 inch. They are also available in most needle sizes, although I have never personally seen a US#0 or a US#19.1
When used in the round, a circular needle can be used for almost any circumference equal or greater than its own length without any special techniques or knowledge. The only limit to the number of stitches is how crowded the filament is. Extremely crowded circular needles are difficult to use, especially with bulky yarns. Fine yarns can be compressed much more easily, and do not pop off the tips at the least provocation. However, placing 40 inches of stitches onto a 32 inch needle is usually fine. Point protectors help keep projects on needles, but a circular needle doesn’t need them unless it is severely overloaded. Simply push the stitches back from the tips as far as they will go and fold the tips under. Your stitches won’t go anywhere.
Many new knitters think of circular knitting needles as something just for knitting in the round; sleeves, hats, socks, tube scarves, the seamless yoke and body of a sweater, etc. They are certainly perfect for knitting in the round. Unlike double pointed needles, there are no needles to drop, no worrying about ladders where the needles meet, no worrying about having too many stitches or dropping stitches from a needle not in use. And they don’t require any juggling of tips and points as 4 or 5 needles clatter together on a sock. However, a circular needle is also perfect for straight or flat knitting, which is commonly done on two single pointed straight needles. Fewer pieces means fewer pieces to lose. It is more compact and thus more portable, and it won’t prod your neighbor on the bus. And, for large projects, it means that the weight of the growing fabric does not sit on the needles as you pivot and turn them, but instead rests in your lap. If your project is extremely large, such as a 6 foot wide extra bulky weight afghan, then 2 long circulars will allow you to cast on the entire width. Just cap the unused ends with point protectors or rubber bands, and use them like very long flexible straight needles.
How to use a circular needle to knit in the round
Cast on your required number of stitches.
Spread the stitches out onto the entire needle so that the beginning of the cast-on and the end of the cast-on are about an inch from the points of the needle tips. Make sure that the cast-on row is not twisted.
Hold the tip with the first cast-on stitch in the hand off of which you knit. I am right-handed and I knit off of the left-hand needle and onto the right-hand needle. So I would hold the tip with the first cast-on stitch in my left hand, and the tip with the last cast-on stitch, which has the yarn dangling from it, in my right hand.
Bring the tips together, place a marker on the needle between the first and last cast on stitches, and start knitting. The tips and the filament form a closed loop, with the needle tips closest to you and the loop of cable hanging from your hands. It should not be between you and the needle tips. If you are right-handed, or a lefty who knits right-handed, you will be knitting every row from right to left. This also means that charts need to be read always from the same side (right to left for right-handed knitting).
Keep in mind that you are always on the right side of your knitting, never the wrong side, unless you inadvertently knit the tube inside out. Because you will always be approaching your knitting from the same side of the row (again, right to left in my case) if you are a combined knitter your stitches will not be sitting on the knitting needle the same way as if you had turned the fabric. They will be sitting on the needle angled backwards from what you would normally see. Just be sure to knit the stitch from its leading edge, unless you are intentionally twisting it, and you will be fine.
Using 1 circular needle for a small circumference.
Say you have a 32 inch circular needle in the right size, but you need to make something 16 inches in circumference. Or, even worse, you are making a hat and it is worked in the round decreasing from 16 inches to no inches. Say you don’t want to buy extra needles. Can it be done? Yes, as long as your knitting needle is long enough.
The larger the circumference, the easier it is to use a too-long needle. Longer needles actually work better, and I find 32 inch about as short as I can go comfortably for a hat. The trick is to put at least one loop into the filament of your circular needle. As you knit, the loop takes up the extra length of the needle, while allowing your stitches to sit close together and without significant stretching. If you are working on a very few stitches, you will need to put in 2 loops in order for the needle tips to have full range of motion.
This can be done in 2 ways, you can either pull out a length of the filament from between 2 stitches or you can force the filament into a loop periodically as you knit the row. I prefer pulling out a length as forcing the loop tends to make the stitch immediately before the loop extremely tight. This is due to the stitch sitting over the filament rather than the needle tip as the next stitch is worked.
If you pull a loop out, it will usually not cross over itself, but instead form a U shape. This will stretch your knitting, so rotate or roll one of the needle tips until the loop ‘pops’ into a circle, crossing over itself. I find that it works best if the loop is on the inside of the larger filament circle. Since I knit right-handedly, I also prefer the lower part of the loop to lead to the left needle end. It is crossed on top by the end of the filament leading to the right hand needle. This allows the loop to sit on top of my left hand as I knit all the stitches up to the loop crossing. Otherwise, the loop would be in the way as I try to knit those stitches.
Placing a loop need only be done about once per row (twice for smaller circumferences). Every time you come to a loop in the row, and thus un-create it, make a new loop to replace it. Choose somewhere close to your most recently knit stitches, so you can knit for as long as possible without placing another loop.
Using 2 circular needles for any small circumference
While one circular needle can be used for any reasonable circumference greater than its length, and long ones can be made to work for smaller circumferences, there is an alternative to the loop method which some people prefer. 2 circular needles can be used much like double pointed needles in order to knit a tube of any circumference. They do not need to be the same length, however keep in mind that long needles can flop and be annoying.
This exercise demonstrates one technique. This only works if the circumference is at least twice the length of the needle tip.
Cast on 60 stitches onto the 1st circular needle (needle A).
Begin knitting in the round by knitting onto the 2nd circular needle (needle B). Do this by holding the last stitch cast on next to the first stitch cast on, this will prevent a loose loop of yarn from gaping there once you finish. Since you are not using the same circular needle to close the loop, the excess length of needle A will not interfere with you as you knit onto B.
As you knit, each row will end with all of the stitches having been transferred to the other needle.
This technique can be used for any circumference, regardless of how small:
Cast on 20 stitches onto the 1st circular needle.
Move the last 10 the stitches to the 2nd circular needle. The first needle is needle A with stitches a, the second needle is needle B with stitches b.
Fold the cast on row in half so that needles A and B are parallel, and the stitches line up.
Shift stitches a towards the end of A off of which you will be knitting.
Take the free end of A and begin knitting stitches a using the yarn still hanging off the last stitch of b.
When you finish knitting all of a, repeat with B, taking the free end of B and knitting all of b.
How to use a circular needle for flat knitting.
This is an easy thing to do which nonetheless stumps many people the first time they try it.
This is identical to knitting with 2 straight needles, only the ends of the needles are connected. It may be helpful to tie the ends of a pair of straight needles together with a long piece of string to get the idea.
Cast on your stitches. Leave the stitches on that end of the circular needle. Switch the current right-hand tip to the left hand and the current left-hand tip to the right hand. Knit the row. Again, leave the stitches on that end of the needle, switch hands, and knit the row.
Keep in mind that you can put many stitches more onto a circular needle than a straight needle. The filament permits cramming stitches together. However, this isn’t always a good idea, especially if you overload the needle to the point that stitches fly off whenever you put it down.
So, you put down your knitting and now don’t know which way you should be going? Look at which stitch has the yarn dangling from it. That will be the last stitch you knitted.
1 Someone tells me that she's seen US#19s and her mother in law had a 70'' long needle custom made for making afghans. These things do exist, although you may not be able to find them at your local yarn shop. I've seen more 40'' needles of late, as well. I've also seen 60'' long US#36 Addi Turbos advertized.
Erlich, Lola ed. Vogue Knitting: the ultimate knitting book, Sixth&Spring Books, 2002.
My own head
Please note, there is a book out there called Socks Soar on Two Circular Needles, by Cat Bordi. I have never read it, but I’ve heard about it in a general sort of way. There is also a pamphlet out about the Magic Loop Technique, which I have never read, but yet again have heard about in a general sort of way. As far as I am aware, what I have described above has been around since the dawn of knitting, and most competent knitters can figure it out for themselves given enough time and the need.
After talking to my sister, and to Swap, about whether it is possible to knit 2 socks on 1 circular needle at the same time, we've discovered that it apparently is. The technique used is the Magic Loop. Directions available as a pdf file: www.knitaddicted.com/html/185.html
There is a lot more out there on circular knitting. This is just what I do, and not an exhaustive review by any means. If there is something you would like me to add, please let me know and I will!