Shuokecrafts 2Pcs O Ring Binder Mechanism, top-binding on the 8.5” edge of a letter size page ,30mm Capacity, 123mm=4.84 inch overall length, 20mm Base, No Boosters ; The time tested and durable design ensures years of use at home, school, and in the office. These are great for those who want to create their own custom binder