These thin cross-section bearings use 4.5 mm diameter BBs as the rolling elements. I designed them to be used, in pairs, for rotating turrets. I've included stl files of the cages and races for 2 different outer diameters : 60 mm and 90 mm. The 60 mm OD size seems like it will work for most 1/144th scale Battleship turrets (12" guns and up.) The 90mm one is for 1/96th scale models. To allow the maximum size through hole, in the center, mounting holes and flanges were not included. They will have to be glued in place. Each bearing uses 3, 3D printed, parts : a cage, an inner race, and an outer race. Using concentric in-fill on the top layers helps them rotate smoothly. A little bit of grease helps to keep the BBs in place, during assembly.