Rayson WR2119BK Wire Binding Spines, 2:1 Pitch Double Loop Binding Wires 3/4 Inch, 21-Loop Wire Ring Pack of 50 with Black : Amazon.co.uk: Stationery & Office Supplies
GBC Binding Wire Element A4 12mm 21 Loop Black (Pack 100) IB165320
5/8 Inch 23 Loops Double Wire O Binding Ring 21 Metal Double Loop Wire with Box Packing - China Double Wire Binding, Double Wire in Spool | Made-in-China.com