According to the △ vs value of plastics, the shrinkage characteristics of various plastics are divided into four groups. The group with small △ vs value is the high-precision group, and so on. The group with large △ vs value is the low-precision group. Precision technology, 110, 120, 130, 140, 150 and 160 tolerance groups are compiled according to the basic dimensions. It is also stipulated that 110, 120 and 130 groups can be selected for the dimensional tolerance of plastic parts formed with plastics with stable shrinkage characteristics.

用收缩特性中等稳定的塑料成形塑件的尺寸公差选用120、130和140。如果用这类塑料成形塑件的尺寸公差选用110组时，即可能出大量尺寸超差塑件。用收缩特性较差的塑料成形塑件的尺寸公差选用130、140和150组。

The dimensional tolerances of plastic parts formed with plastics with moderate and stable shrinkage characteristics are 120, 130 and 140. If 110 groups are selected for the dimensional tolerance of plastic parts formed with this kind of plastic, a large number of plastic parts with out of tolerance can be produced. The dimensional tolerances of plastic parts formed with plastics with poor shrinkage characteristics are 130, 140 and 150 groups.

模具型腔和型芯的加工尺寸除了通过D=M(1+S)公式计算基本尺寸之外，还有一个加工公差的问题。按照惯例，模具的加工公差为塑件公差的1/3。但由於塑料收缩率范围和稳定性各有差异，必须合理化确定不同塑料所成形塑件的尺寸公差。

In addition to calculating the basic dimensions through the formula d = m (1 + s), there is also a problem of machining tolerance. According to the Convention, the machining tolerance of the die is 1 / 3 of the tolerance of the plastic part. However, due to the differences of plastic shrinkage range and stability, it is necessary to reasonably determine the dimensional tolerance of plastic parts formed by different plastics.

即由收缩率范围较大或收缩率稳定较差塑料成形塑件的尺寸公差应取得大一些。否则就可能出现大量尺寸超差的废品。为此，各国对塑料件的尺寸公差专门制订了标准或行业标准。也曾制订了部级标准。

That is, the dimensional tolerance of plastic parts formed by plastic with large shrinkage range or poor shrinkage stability should be larger. Otherwise, a large number of waste products with out of tolerance may appear. Therefore, countries have formulated national standards or industrial standards for the dimensional tolerance of plastic parts. China has also formulated ministerial standards.

但大都无相应的模具型腔的尺寸公差。德国标准中专门制订了塑件尺寸公差的DIN16901标准及相应的模具型腔尺寸公差的DIN16749标准。此标准在世界上具有较大的影响，因而可供塑料模具行业参考。

But most of them have no corresponding dimensional tolerance of die cavity. Din 16901 standard for dimensional tolerance of plastic parts and DIN 16749 standard for dimensional tolerance of die cavity are specially formulated in German national standards. This standard has great influence in the world, so it can be used as a reference for plastic mold industry.