uxcell Nitrile Rubber O-Rings 33mm OD 30mm ID 1.5mm Width, Metric Sealing Gasket, Pack of 10: Amazon.com: Industrial & Scientific
Amazon.com: uxcell Nitrile Rubber O-Rings, 30mm OD 28mm ID 1mm Width, Metric Buna-N Sealing Gasket, Pack of 20 : Industrial & Scientific
Amazon.com : Shuokecrafts 5Pack Top-Binding Rings Binder Mechanism,2 D-Rings, 30mm Inner Height, 26mm Base Width,133mm= 5 .24 inch Overall Length, Used for 8.5” Edge of a Letter Size Page, No Boosters :