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This is a STL for a fidget spinner I designed using 6 mm BBs. Its designed to be spun on your finger (diameter of middle is around 15mm.) I used the Cura plugin "Pause at Z height" and paused the print around 5.4 or 5.5 mm, then pushed the BBs in. Make sure you have good bed adhesion otherwise it could move while your pushing the BBs in.
Make sure your printer is calibrated properly (use calibration cube.)
Will add smaller one in future for smaller fingers. This is is about 4 inches in lengh and can be made smaller.