ASTM D2266 for wear preventive characteristics of lubricating grease
ASTM D2266 standard test method for wear preventive characteristics of lubricating grease (Four-Ball method)
4. Summary of Test Method
4.1 Three 1/2 in. (12.7-mm) diameter steel balls are clamped together and covered with the lubricant to be evaluated. A fourth 1/2 in. diameter steel ball, referred to as the top ball, is pressed with a force of 40 kgf (392 N) into the cavity formed by the three clamped balls for three-point contact. The temperature of the lubricating grease specimen is regulated at 75°C (167°F) and then the top ball is rotated at 1200 rpm for 60 min. Lubricants are compared by using the average size of the scar diameters worn on the three lower clamped balls.

NOTE 1 - Because of differences in the construction of the various machines on which the four-ball test can be made, the manufacturer's instructions should be consulted for proper machine setup and operation.

NOTE 2 - Although the test can be run under other test parameters, the precision noted in Section 11 can vary when testing with other than test parameters listed in Section 8.

5. Significance and Use
5.1 The four-ball wear-test method can be used to determine the relative wear-preventing properties of greases under the test conditions and if the test conditions are changed the relative ratings may be different. No correlation has been established between the four-ball wear test and field service. The test method cannot be used to differentiate between Extreme Pressure (EP) and Non-Extreme Pressure (Non-EP) Greases.