[Not Compatible with Office 3 Ring Binder] K-KEEP [Binder Backboards] - For [A4 Standard] 4-Ring Binder - Protect Your Collectible From Bending (2 Pcs Per Pack) - D-048

This Backboard has holes pouched in a way that can only work for A4-4-Ring Binder This is NOT Going to work for the American 3-Ring Office Binder. However if you owned some A4-4-Ring Binder and is searching for backboard this is a good choice for you!  [A4 Standard] - 2 Pcs Per Pack - Protect Your Collectible From Bending | Pro Binder Accessories   Thickness: 1MM Dimension: 230x300mm