A screw post (also called a binding post or a Chicago screw) is made up of two separate pieces – a threaded post attached to a head and a cylinder attached to a matching head. To create a bound item, a hole is first punched through the documents to be bound. The cylinder is inserted into the hole, and then the threaded post is inserted into the cylinder and tightened. Because the heads are of a larger diameter than the hole, the documents remain securely bound between them. To make changes within the bound document, simply unscrew the threaded post from the cylinder, insert your revised documents, and reassemble the screw post.