Even after over 50 years on the market, the binding system for plastic bindings is still considered one of the best methods for binding documents. The flexible and cost-effective system meets the needs of most users, from students to professionals in large companies. It gives bound documents a professional appearance. Durable, premium-quality plastic binder spines. The most popular, economical, and flexible binding method. 6 mm binder spines suitable for 21 to 40 pages. 21 rings, white, round. Pack size: 25 pieces. Compatible with any plastic binding machine with 21 rings for binding up to 40 sheets.