Apparently, there are at least two major kinds of wire binding in use for notebooks & printed matter these days. Spiral binding is what you remember from cheap 80 page notebooks in highschool and those little flip-top notepads. Double loop binding still uses a single piece of wire, but uses it to form something like doubled "teeth" which pass through the holes in the paper. It's a bit tricky to describe, but you might have seen this on higher-end sketchbooks or calendars.

RiteInTheRain does this.