The typical four-ball test method rotates a 1/2-inch steel ball on top of a cluster of three stationary balls immersed in the fluid to be tested. Examination of the size, appearance, and other characteristics of the wear scar produced on each of the lower balls, taken in conjunction with the friction trace produced by the test machine, reveals characteristics of the test fluid as a lubricant. The images at right are examples of four-ball wear scars from AAT&D's quality-control testing of specialized lubricants. Ann Arbor Testing & Development, Inc., specializes in using four-ball test methods (as well as other testing using ASTM methods).