The differences between shouldered and shoulderless tools in the micro-friction stir welding of 0.8 mm thin plates were evaluated. Employing a suite of advanced characterization methods, including white light interferometry, electron backscatter diffraction (EBSD), and scanning electron microscopy, the formation of weld surface, joint microstructure distribution, and fracture characteristics were studied. The enhancement mechanism of mechanical properties was explained through the Hall-Petch relationship and Taylor''s hardening law. Results indicate that the main reason for the increased yield strength observed in shoulderless tool joints is the combined mechanism of dislocation strengthening and fine-grain strengthening. Specifically, the utilization of shouldered tools results in a smooth weld surface, with an average grain size of 11.24 μm and a high-angle grain boundary content of 16.80% in the nugget zone. The primary texture components are the {011}<100> Goss and {112}<111> copper textures, yielding a maximum texture strength of 3.70. Simultaneously, the fracture dimples exhibit a reduction in size and an increase in depth. Whereas the welds produced with shoulderless tools display slight burrs on the surface. The experimental results demonstrate that the average grain size in the nugget zone of these joints is significantly reduced to 0.59 μm, while the high-angle grain boundary content reaches 34.34%. This process is accompanied by the formation of {111}<110> Shear textures and {001}<110> rotated cubic textures as the main components, resulting in a significant increase in maximum texture strength to 6.65.