An oil seal normally consists of three components: The Sealing Element (the nitrile rubber part), the Metal Case, and the Spring. It is a widely used sealing component. The function of a seal is to prevent the leakage of medium along the moving parts. This is mainly achieved by the sealing element. Nitrile Rubber. Oil Seals are Designed to aid trouble-free operation of your equipment, providing an excellent barrier against the escape of oils and greases. Other sizes may also be available but may not be displayed please contact us if you require a size not displayed on our shop.