Basically spiral binding just consists of a screwy wire passed though a series of holes up the spine of the book. This picture from MGX Copy in San Diego illustrates it clearly. Of course the inserting will be by machine, not in this handcraft fashion. Spiral is the most common type of mechanical binding.

Mechanical binding. There are four primary types of mechanical binding: spiral binding, metal wire binding, plastic comb binding, and loose-leaf binding. One might argue that side-wire binding should be included under the mechanical rubric, but it’s not. The commonality appears to be the drilling of holes. It’s not clear where the term mechanical binding comes from: paradoxically mechanical binding is in essence the least mechanized method of binding a book. One might hypothesize that in the dim and distant there was a moment when these methods had been developed while most book binding was still hand binding. Not sure that makes any sense though. Maybe the term originates in the office where it might be regarded as more mechanical than just putting a rubber band round a bunch of pages, and the term stuck with the methods when they moved into the bindery. Just like “perfect” as an epithet is applied to the far from perfect perfect binding method, we may regard “mechanical” as unintentionally ironical.

The thickness of book you can bind via spiral binding is governed by the availability of wires, which may be metal, plastic or plastic-coated metal, so the fattest book you can spiral bind is ⅞”. This style of binding will be used for a book which has to lie flat when opened. However when the book is opened the facing pages will not align because the one on the left will be a little bit further up the spiral wire. If this is a problem, look elsewhere.

For other binding styles please search for “binding styles”.