Plastic comb binding is an economical and simple binding method. Made of PVC plastic, the combs consist of a spine of rings that spread open using a comb binding machine for sheet inserting. The standard length of a binding spine is 11" for letter size sheets, and features 19 rings that fit into rectangular holes. Plastic comb binding is perfect for those who will need to frequently edit their documents because the bindings can easily be opened and closed without damaging the contents or comb binder. Comb binders are popular for cook books, manuals and classroom children's books because you can get them custom printed on the spine for labeling.