As is often the case with dimensional tolerances, the dimensional tolerances of plastic processing are different from those of metal.
Tolerances on plastic are harder to achieve than on metal.
The primary reason for this is that the heat generated by plastic is several times greater than that of metal, and the temperature difference between processing and use of the part results in dimensional variations. Also, unlike metal, the blades used are not as hard, so care must be taken to avoid blade chatter.
Metal can generally be toleranced to 1/1000 mm, but plastic is difficult to tolerate, and the limit is in the 1/100 mm range.
The tolerances in the 1/1000 mm range (h7,H7) for hole and fit tolerances are often seen in drawings from designers and developers. Since these tolerances are impossible to manufacture with plastic, we will always have a meeting to confirm them, but in general, we would like you to use the middle level of JIS as a guide.

Among plastics, there are cases in which dimensional variations become large depending on external factors such as temperature and humidity.
For example, MC nylon has a higher water absorption rate than other plastics, and there have been cases where dimensions have changed by more than ±0.5 mm between dry and rainy seasons. Even if the dimensions are as shown in the drawings at the time of processing, care must be taken when the product is delivered in an environment with different humidity and temperature.