The freight railway industry relies on the interchangeability of coupling system parts (i.e., couplers, locks, throwers, pins, knuckles). Variability in the dimensions of the components affects the ability to change parts efficiently and the performance of the components. Because of the complex shapes and dimensions involved, it has been difficult to identify the component causing most of the problems for a combination of coupling system parts. Transportation Technology Center Inc. (TTCI) has developed a digital E-type coupler gage that can be combined with 3-dimensional scanning technologies to help railroads and manufacturers find areas that may be causing fitment problems. Physical gages are also being developed for use in production and field environments. The digital and physical gages can be used for fitment quality checks by the railroads and manufacturers. The digital gage requires a laser scanning of the coupler in question to be completed. A 3-dimensional scan of a coupler can be overlaid with the digital gage to find the dimensions causing a problem. Though it is currently a destructive method, further development of scanning technology could make the process more efficient and nondestructive. Using a combination of the digital and physical gages with the proper procedure may reduce the number of problems with properly fitting components and premature failure of couplers in service.