Quantity: 1 set (270 pieces). 1 x Set Rubber O Ring. We will be happy to resolve any issues you may have in a cordial and friendly manner. Otherwise deal is final. Hydrogenated Nitrile Butadiene Rubber (HNBR), also known as Highly Saturated Nitrile (HSN) is special class of nitrile rubber (NBR) and is for mission critical applications.