Durable Metal Construction for Long-Lasting Use. Binding with 3:1 coil binding spiral or 3:1 wire-o binding ring;
3:1 Coil binding ring means per inch has 3 holes (This is very important distinguish 3:1 from 4:1 cause the things to be as different. 4:1 means per inch has 4 holes. They are used with different binding machine.)