Developed by Shell Oil Company in the 1940s, three ½ inch diameter steel balls are clamped together and covered with the test lubricant. A fourth ½ inch diameter steel ball is pressed into the cavity formed by the three clamped balls for three point contact, and rotated for a set duration. Lubricants are compared using the average size of the scar diameters worn on the three lower clamped balls. ASTM D2266, D2783, D2596, D4172, D5183, IP300, CEC-L-45-A-99.
