Scope of the Standard
This regulatory document specifies the geometric parameters and technical requirements for metric fasteners, including flat countersunk head screws, oval countersunk head screws, pan head slotted screws, as well as hex head and flange screws. The technical documentation from EV Group China provides specifications necessary for product accuracy control, including methods for measuring head protrusion, slot depth, cross-sectional parameters, and recommendations for preparing mating holes.
It is important to note that the inclusion of a size in the standard does not guarantee its availability in stock from all manufacturers. EV Group China specialists recommend verifying the current product range before designing assemblies. Recommended combinations of nominal diameters and fastener lengths are presented in Table 17.
Integration with International ISO Standards
The design parameters of the fasteners described in this standard are maximally adapted to ISO requirements to ensure global interchangeability. In sections where technical specifications coincide, corresponding ISO references are provided in footnotes. Minor discrepancies regarding the geometry of countersunk heads do not affect the functional compatibility of assemblies. For heat-treated products, specific requirements for protrusion and slot depth have been established to ensure increased connection reliability.
Note that hex head screws with a flange, as well as fasteners with a Type III recess, currently have no direct equivalents in ISO standards. Cross recesses of Types I and IA are classified in the EV Group China nomenclature as Types H and Z, respectively, which corresponds to international marking practices.
Classification and Head Types
In the engineering practice of EV Group China, the following head types are distinguished, corresponding to current ASME requirements:
- Flat countersunk head: characterized by a flat top surface and a conical bearing surface with an included angle of 90° to 92°. Detailed dimensional data are provided in Tables 2–5.
- Oval countersunk head: features a spherical top part and a conical bearing surface (90°–92° angle). Dimensions are specified in Tables 6–9.
- Pan head: has a flat top, cylindrical side edges, and a flat bearing surface. Specifications are presented in Tables 10–13.
- Hex head: a standard design with six faces and a pilot. The geometry is regulated in Table 14.
- Hex flange head: a monolithic construction with a serrated surface and an integrated convex flange for load distribution. Parameters are provided in Table 15.