Many factors influence the final geometry of 3D printed parts. These factors include model file export settings, slicer settings, material and printer quality, part geometry, cooling, etc. This paper is based on experimental determination of 3D printed part geometrical tolerances and the parameters which influence them. The research presented examines the dimensional tolerances, roundness and concentricity of 3D printed round holes used for bearing seats in order to determine the influence of the geometry on the fitment that can be achieved using nominal size values. Parts are printed on a commercially available 3D printer out of PET-G filament and then measured using an Absolute Arm-a 7-Axis to collect dimensional data. The experimental data is used to determine the necessary settings and nominal dimensions needed in the modelling, exporting and slicing phases in order to achieve a clearance or interference fit between a cylindrical part and a cylindrical hole made on an FDM 3D printer.