Unlike modern knitting naalbinding requires only a single needle. Typically between 2.5 and 5.5 inches, though other sizes are used and many people simply use commonly available, blunt tapestry needles.
This Instructable shows how I made one of bone, similar to a number of examples from archeological sites from Northern Europe and Scandinavia. Mine is definitely on the small side. Though, I haven't developed a preference for one size or another, it should not be taken as "correct" or even preferred but rather, just an example of one you might make. Either way it certainly does the job.
It does seem that most modern naalbinding needles tend to be on the longer side of the range with 5 or more inches being common and I have seen at least one stitch where a longer needle would probably be an advantage.
To do the knitting itself please see these excellent Instructables
Knit like a Viking
On to making the needle...
Step 1: Materials and tools
A rotary tool with a cutoff wheel and sanding attachment.
A pocket knife
A drill with a small bit
A sanding block
Beeswax for the finish
You might want gloves and a dust mask is more than a good idea any time you are working with bone. The dust tends to be very bad for your lungs.
Step 2: Basic shape
I looked at quite a few examples of historic needles and went with a shape that was close to a number of them. These are basically just flat blunt bone needles so it isn't all that complex. Again, I made one on the short side of the range.
This is all entirely up to you if you decide to make one of your own. Wood and antler are other common materials but you could even use a toothbrush if you wanted to!
Step 3: Roughing it out
Once you have your rough shape you can progress to something that looks more like the end product. I used a knife at various points throughout the process but if you aren't used to this it really isn't necessary. The rotary tool and sand paper will do just fine all by themselves.
Step 4: Further shaping
Once you get your shaped dialed in you can do the gentle final shaping. This is the stage where you will want to feel all over the needle to make sure there is nothing to snag your yarn.
Step 5: Drilling and finishing
For the final finish I used wax. Warm it up and rub or drip it over the needle to fill the pores and provide a smooth surface that won't snag. You could even use regular candle wax for this.
Essentially any woodworking finish is fine for bone. So, if you are familiar with using something like Linseed or Tongue oil, by all means do. The important part is a smooth finish, not what you finish it with.
In the photo I'm using the knife to make a small pilot hole. It's just a matter of picking a spot and spinning the point of the blade like a drill. Be careful to leave enough distance from the back edge so you don't drill through it.
Step 6: Ready to knit!
You can easily purchase bone needles online for as little as $5 plus shipping but I wanted to make my own and to bring my naalbinding experience full circle.