Thick intermediate films or third bodies with high load-carrying capacity are generated through wear by different materials. A balance thus naturally exists between the material wear rate and the protection afforded by these compacted wear debris films. The length of a specimen situated parallel to the sliding motion or wear debris transport direction, necessarily plays a role different from its width. For the same unit, loading material wear protection increases with length and is independent of width. The wear problem can, therefore, be approached with two-dimensional models. Debris motion explains why wear data obtained with the same materials on machines with specimens of different shapes are difficult to correlate.Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Kansas City, Missouri, October 3–5, 1977