This O-Ring kit includes 990 pieces of high quality Nitrile Rubber O-Rings, all made with a 70A Durometer for durability. The round cross section design makes them perfect for various applications, including pressure washers, plumbing, air and gas seals. These synthetic rubber gaskets come in 20 different sizes, ensuring a perfect fit for any project. They are heat and oil resistant, making them ideal for a wide range of uses.