Features GREAT MATERIAL Made of high quality plastic with pretty color, not easy to deform and very durable in corrosion and long time use. BETTER BINDING Easy to install and remove. You can also cut the binding comb to the desired length to meet your storage needs. FOR YOUR PAPER The spiral binding spool has an inner diameter of 13mm and allows for smoother turning of pages for reading and writing. LARGE CAPACITY The binder spine can hold a large amount of sheets and is perfect for office, classroom, library, etc. Total 20 pieces: the set includes 20 pieces spiral binding spools, and the large quantity makes it easier to replace damaged bobbins. Specification: Item Type:Spiral Binding Spool Inner diameter: approx. 13 mm / 0.51 inches. Type: Stationery Accessory, Binding Accessories Package list: 20 x spiral binding spools. Package List 20 x Spiral Binding Coil