QC/T 518-1999 in English

Scope

This standard specifies the tightening torque of fasteners with thread diameters of 6mm to 20mm for automobiles. This standard applies to tightening by controlled torque that meets the following conditions:
　——The mechanical properties of external threaded parts comply with grades 8.8 and 10.9 specified in GB/T 3098.1;
　——The mechanical properties of internally threaded parts comply with GB/T 3098.2 or GB /T 3098.4, and has the strength to fully utilize the load-bearing capacity of the threaded connection pair;
　——The thread complies with GB/T 196, and the thread accuracy is not less than level 6 specified in GB/T 197;
　——The hexagonal dimensions of the internal and external threaded parts comply with Standard series specified in GB/T 3104;
　——The surfaces of internal and external threaded parts are in the state commonly used in the automotive industry;
　——Externally threaded parts bear axial tensile load during tightening. This standard does not apply to set screws whose external threads bear compression force during fastening, self-tapping screws and wood screws whose threads are attacked by external threads, threaded fasteners using spring washers or elastic washers, and effective torque type threads. Tightening of fasteners. When the surface conditions are different, the size and shape of the supporting surface are greatly different from the standard conditions, so that the pretightening force cannot meet the requirements or there are special requirements for the pretightening force, the tightening torque should be adjusted. Note: 1 For the load-bearing capacity of threaded connection pairs, see Appendix A of GB/T 3098.2. 2 Effective torque—the rotational moment measured when the bolt or nut is rotated smoothly when the threaded connection pair does not bear axial load.