Made of Buna-N, these O-rings resist grease, hydraulic oil, and motor oil—plus mild chemicals and water. However, Buna-N is not for use with brake fluid. These O-rings are commonly used to create multidirectional seals between two parts in power transmission assemblies, hydraulic cylinders, and pneumatic cylinders. With a round profile, they resist compression and tearing to keep their shape over time, so they’re reusable. All have shelf life, cure date, and a traceable lot number printed on the bag. Many meet ASTM D2000 and SAE J200, international standards for rubber products.