Even after more than 50 years on the market, the plastic binding system 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. Gives bound documents a professional look. Durable plastic binding spines with premium quality. The most popular, economical and flexible binding method. 12mm binding spines suitable for 21 to 40 pages. 21 rings, white, round. Pack size 25 pieces. Suitable for any plastic binding machine with 21 rings for binding up to 40 sheets.