Wire-O Binding, also known as Twin Loop, Double-Loop, Double-O, Duo-Wire, or simply Wire Binding, is a popular method for joining the pages and cover of a bound document.
Wire-O binding offers many of the same benefits as spiral coil binding, but is more sophisticated in appearance. As such, it produces a very impressive document. Also, it can accommodate pages and inserts of varying thicknesses, including dividers or index tabs made from heavy cardstock.
The pages can be opened a full 360 degrees. A Wire-O bound book can fold all the way back upon itself and yet still remain flat, so it provides for easy reference while taking up minimal room on a desk or table. This makes Wire-O binding an excellent choice for reports, directories, cookbooks, music books, instructional books and maintenance manuals. Atlases and travel guides are also commonly Wire-O bound because they are easier to manage when traveling. And because they can open fully, it prevents important information from getting buried near the book's spine.