Wire binding is a method in which holes are punched along the side of a page and inserted onto a wire, which can be a different size, colour and pitch being 2:1 and 3:1 to be used with different machines.
Wire binding allows you to open the document fully on a desk and also has 360˚ rotation. They also come in A5 and A4 layout.
2:1 pitch is most commonly used for binding larger diameter documents but can also be used for smaller ones too. They come in a variety of sizes from 6,9mm up to 38mm, they come in a variety of colours most common being Red, White, Silver and Black.
3:1 pitch is mostly used for binding smaller diameter documents and sizes coincide with that, as they range from 8,47mm up to 16mm they also come in the same colour range as the 2:1 pitch.