The number of strands of beading wire is a function of how pliable it is but even that is dependent on the gauge of the wire. But just for simplicity sake, think that if you put 49 strands in the same space as the one with 7, then the 49 strands are much thinner, and thus much more pliable.
It gets even more confusing, we can thank the fact that the wire we use wasn't originally made for beading. It was made for Fishing! (that's right Fishing) in fact one of the major manufacturers of our beading wire still sells fishing wire.
So to confuse us more, it is measured it in gauges. Gauge is a measurement of the wire diameter, and in electrical terms, this size determines the amount of current a wire can carry. And exactly what does this have to do with beading? One day I have to research this.
And to make it even more confusing, the smaller the number, the larger the wire, which I assume has something to do with electricity.
And then we measure beads in millimeters....because well, that's how they are made and let's face it most of the world works in millimeters. So we will just have to teach you this. For example 10mm, well take a look at your pinky finger, the nail on that finger is more or less 10mm. Our bead sizes are noted in millimeters diameter. Then remember that 25mm equals 1 inch, so essentially the size of a 1 inch ball.
So wire used for stringing, artistic wire used for wire wrapping and headpins are all measured in gauge. Common gauges for headpins is 20, 22 or 24. (Remember the larger number is the more flexible because it is the smallest.)
10 Gauge = 2.59mm (0.1019 Inches)
20 Gauge = 0.813 (0.032 Inches)
So here is a conversion from Wire Gauges to Inches to Millimeters.
20 Gauge artistic wire is a good size for wire wrapping as it is strong enough to hold up for your designs. And yet is still pliable enough to use.