To gain further knowledge of the wear phenomena in gear tooth flexible couplings, specimens of coupling materials were tested in an apparatus which simulates service conditions. The variable test parameters were load, amplitude of motion, speed, hardness, surface geometry, and lubricant. The wear patterns that were obtained in short-duration tests on this machine duplicate those found in service. A common gear steel, SAE 4140, was chosen as a standard material, and curves of wear versus load and amplitude of motion were generated for three different hardnesses of this material in a bath of 2190 TEP oil. Further investigations were made on ways to improve the performance of this material. These included special surface treatments, different lubricants, crowning of the surfaces, and other special surface geometries. Several other materials were tested with various crowns to compare their wear properties to that of the standard. These materials included 4340 steel, aluminum bronze versus NicuAl alloy, nitrided AMS 6475, nitrided 304 stainless steel, manganese bronze, CuAlNiFe alloy and worm wheel bronze versus 4140 steel. Of the materials tested, it appears that manganese bronze (Mil-B-16522 Class 1) is the best material for dental coupling use at the conditions of these tests.Contributed by the ASLE Technical Committee on Gears and Gear Lubrication and presented at the Annual Meeting of the American Society of Lubrication Engineers held in Philadelphia, Pennsylvania, April 1961.