SAE: SAE is the abbreviation of the English "American Association of Motor Vehicle Engineers". The label behind the SAE indicates the viscosity of the oil.
API: API is the abbreviation of the English "American Petroleum Institute", and the label behind the API indicates the quality level of the oil.
The meaning of the letters after S or C is: from "SA" to "SN", the environmental protection level of the oil will be better than the former one for each letter. The higher the letter, the higher the environmental rating, the international brand. The oil level is mostly above the SF level, and the oil with the highest environmental protection level is the “SN” level.