GB 197-81 pdf download.General purpose screw threads–Tolerances and fits (diameter from 1 to 355mm).National Standard of the Peoples Republic of China.
This standard is applicable to the thread stipulated in GB 192-81 General purpose screw threads–Basic concepts and symbols for tooth shapes and tolerance zone and GB-81 General purpose screw threads–Diameters and pitches.
GB 197-81 specifies the minimum clearance of thread fit as zero and thread tolerance and fundamental deviation to guarantee the clearance.
The position of thread tolerance zone is decided by fundamental deviation This standard specifies that external thread upper deviation(es) and internal thread lower deviation(El)as fundamental deviation.
It is specified G and H two kinds of position (see Figure 2) for internal thread And it is specified e, f, g and h four kinds of position (see Figure 3) for external thread. The fundamental deviation of H and h are zero the fundamental deviation of G is positive value, fundamental deviation of e, f, and g are negative value.
Value of fundamental deviation stipulated in Table 1.