A fiber has a diameter, including coating, of exactly 125 µm. The ferrule in the connector has a hole for this diameter. During the manufacturing process, the fiber is pushed into this small hole, glued to the ferrule, and then polished. The larger this hole is, the more room the fiber has to move. In our assemblies, we exclusively use ferrules with a hole of a maximum of 125.5 µm. Therefore, our fiber has a maximum play of 0.5 µm. These ferrules are specially selected, as only a few meet these requirements. Ferrules with larger tolerances are, of course, easier to produce and are available in much larger quantities, making them correspondingly cheaper, but they come with much larger holes. The standard ferrules from most suppliers on the market have tolerances of 128.5 µm +/- 1 µm. A simple calculation is enough to explain how negatively this can impact practical applications. Singlemode has a core diameter of 9 µm.