The designation 20x35x7 refers to the dimensions of the oil seal. The numbers represent the inner diameter (20 mm), outer diameter (35 mm), and the thickness (7 mm) of the seal. The design of an oil seal is critical, as it must fit precisely to ensure a proper seal and prevent the ingress of dirt, dust, or moisture. The choice of material used for these seals often includes rubber compounds that enhance flexibility and resilience. Common materials include nitrile rubber (NBR), fluorocarbon rubber (FKM), and silicone, each chosen based on the specific application and operating conditions.