Industrial Lubricants & Grease | By Weight | SAE GRADE
Society of Automotive Engineers, an organization serving the automotive industry, devised a system for classifying engine and automotive gear lubricants according primarily to their viscosity. The SAE Viscosity number classifies crankcase, transmission, and differential lubricants, according to their viscosities, SAE numbers are used in connection with recommendations for crankcase oils to meet various design, service and temperature requirements affecting viscosity only; they do not denote quality.
The number mentioned before the "W" indicates the oil flow at 0 degrees Fahrenheit, which means that the lower that number, the less the oil will thicken in cold conditions. The number after the " W" indicates the oil viscosity measured at 212 degrees Fahrenheit. It represents how quickly the oil will thin out at a higher temperature.
Single-grade engine oils cannot use viscosity modifier additive and have 11 established viscosity grades out of which six are denoted with the letter “W”. These 11 grades are 0W, 5W, 10W, 20W, 20, 30, 40, 50 and 60. Single-grade engine oils are also called ‘straight-weight’ oils.