is either of two lubricant test procedures, the Four-Ball Wear Method (ASTM-D-2266) and Four Ball EP (extreme pressure) Method (ASTM-D-2596), based on the same principle. Three steel balls are clamped together to form a cradle upon which a fourth ball rotates on a vertical axis. The balls are immersed in the lubricant under investigation. The Four Ball Wear Method is used to determine the anti-wear properties of lubricants operating under boundary lubrication conditions. The test is carried out at a specified speed, temperature and load. At the end of a specified test time, the average diameter of the wear scars on the three lower balls is reported. The Four-Ball EP Method is designed to evaluate performance under much higher unit loads. The loading is increased at specified intervals until the rotating ball seizes and welds to the other balls. At the end of each interval the average scar diameter is recorded. Two values are generally reported — load wear index (formerly mean Hertz load) and weld point.