These extensions are designed to attach to Screw posts, also known as Chicago screws or book binding posts, to create a longer length. Screw posts are extremely versatile binders that allow loose documents of practically any shape or size to be securely bound together. Chicago screws enable you to easily change out bound documents, making them a great choice for price books, menus, swatch books, architectural and engineering drawings, and much more. Our aluminum screw posts provide an easy-to-use alternative to other binding methods. Their two-piece construction allows for no-fuss updates, which is why they're an ideal choice for applications that require frequent updates. They are also easy to expand using these extension posts.