Stud bolts without tight fit DIN 939Fo-5.8 zinc plated blue M6x25mm

The number before the point multiplied by one hundred gives the nominal value of the tensile strength in N/mm2, the number before the point multiplied by the number after the point and multiplied by 10 gives the nominal value of the lower yield strength in N/mm2. The number after the decimal point provides information about the yield strength, as a percentage of the tensile strength.

Free-cutting steels are described in ISO 683-4. A distinction is made between grades not intended for heat treatment, those intended for case hardening, and free-cutting steels intended for tempering. All steels in accordance with ISO 683-4 are easily machinable (turning, drilling, milling) due to their chip-breaking properties. Tensile strengths range from 310 to 900 MPa, depending on the heat treatment.

Blue galvanised finishes are produced either by electroplating in accordance with DIN EN ISO 4042 or by mechanical plating in accordance with DIN EN ISO 12683. For fasteners with a hardness exceeding 390 HV, there is a risk of hydrogen embrittlement during galvanising (electrolytic process). This necessitates specific measures (such as annealing), although these do not provide a 100 per cent guarantee against embrittlement.