Book ring size: The book rings have an inner diameter of 25mm and an outer diameter of 30mm. The common size of 50 pieces suits your processing needs for small items. SIMPLE OPERATION: The binding ring consists of 2 parts and is connected by a very easy-to-use rotating rivet. Just pull it to open and push to close. DURABLE AND HEARD: Made of metal with a nickel-plated finish, tough and sturdy, tightly closed, ideal for storing loose items that organize your books. Wide Applications: Wide range of uses such as scrapbooks, loose-leaf notebooks, memo archiving, photo albums, key rings and sample holders. You can easily link loose objects. Characteristics: 1) Jump rings with a capacity of 2.5 cm / 1 inch hold up to 170 sheets, 50 pieces are required for their output 2) The tight interlocking of the design keeps your books organized and not scattered after they collapse 3) Can be used for folder, study or message cards, classroom, office, home, keychain, etc. 4) Usage: hands crossed and imposed. Technical specifications: Material: iron. Inner diameter: 25.4 mm. Outside diameter: 30 mm. Package content:50 book rings. Warm tips: 1. The loose-leaf binders are small parts that are not suitable for children under 3 years of age. 2. Do not leave your children alone to use the book rings under adult supervision.