Modern machine manufacturers are making the design and technology of their products more and more complicated. This is to protect against a frequently used practice at customers, i.e. making extra parts on your own. This is because entrepreneurs often cannot afford to order expensive original spare parts and - using reverse engineering - prepare working drawings and commission the components to be made in their own machine park or externally from local suppliers. However, the matter is more complex in the case of gears, which so far have been designed on the basis of the selection of standard geometric parameters. A small modification of one or more of these parameters is enough and it becomes very difficult to recreate the geometry of such a gear. This paper presents the issues related to the reverse engineering of a spur involute gear with very non-standard parameters m = 4.98, α = 26.325 °, x = 0.0695, y = 0.795, c* = 0.383. Further metrological steps were proposed that should be taken to correctly identify at least the fact that the test object is not a part produced by standard modular tools (Fellows cutter, Maag rack cutter, worm cutter, etc.). The work also includes short graphical analyzes of the recreated geometry.