The corresponding designation says about this.

In implementation, various types of mothers are intended for specific loads. The corresponding designation says about this. For a sleeping room, it is most beautiful to take mother, designed for small loads. The largest cross -country ability is noted in the kitchen and corridor, and therefore very strong material will be suitable here. If we declare classes, then to finish the floor in the inhabited apartment there are enough 21 or 22 classes, and the grade 31-33 is intended for premises of offices and production workshops