This standard specifies the head shape of slotted and cross recessed countersunk head, semi-countersunk head screws and self-tapping screws, and recommends the measurement methods that should be specified in the corresponding product standards. This standard is equivalent to the international standard ISO 7721-1983 "Countersunk head screws-Head shape and measurement". GB/T 5279-1985 Countersunk head screw head shape and measurement GB/T5279-1985 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Countersunk head screws
Head configuration and gauging
Countersunk head screws-
Head configuration and gaugingUDC 621.882.1
GB5279-85
ISO7721-1983
This standard specifies the head configuration of slotted and cross recessed countersunk head, semi-countersunk head screws and self-tapping screws, and recommends the measurement methods to be specified in the corresponding product standards.
This standard is equivalent to the international standard ISO7721-1983 "Countersunk head screw head configuration and measurement". 1 Head configuration, as specified in Figure 1 and Table 1.
dk theoretical maximum
dk theoretical minimum
dk actual maximum
dk actual minimum
Published by National Bureau of Standards on August 1, 1985
Implementation on June 1, 1986
GB5279—85
2 Measurement method, as specified in Figures 2, 3 and Table 2. GB5279—85
The top surface of the nail head must be between surfaces A and B
Gauge for measuring head height
Figure 3 Actual minimum stop ring gauge for measuring dk
Thread specifications
NailM1.6M2
Self-tapping screw
S T4.2ST4.8S T5.5S T6.3
Note: damin is determined based on the screw fillet radius r=0.25d and the self-tapping screw r=0.4d.
B.5410.62
Basic assumptions:
GB5279—85
Appendix A
Calculation of the maximum head diameter of countersunk screws
(reference)
dkTheoretical maximum
dxActual maximum
Gap tolerance between punch and die
When the screw head is made to the minimum height, the gap between the punch and the die is the minimum value C, as shown in the following table:
Thread specification
Self-tapping screws
ST4.2ST4.8bzxz.net
ST6.3/ST8
When the screw head is made to the maximum height and the maximum actual diameter, the head outline and the gap between the punch and the die are as shown in Figure b.
above.
In the figure: S=p-1
And, P= LM= (F+C) sec45°
r=LMtan22°30′ = (F+C) sec45°× tan22°30°So, S=（F+C）sec45°-（F+C）sec45°×tan22°30= (F+C)(sec45°)(1-tan22°30')0.33 (F+C)dkactual maximum=dktheoretical maximum-2S=dktheoretical maximum-1.66（F+C）It should also be assumed that the relationship between the theoretical and actual diameters is roughly unchanged: dactual minimum dktheoretical minimum-(dtheoretical maximum dkactual maximum) Among them, dtheoretical minimum ~ dktheoretical maximum-2F. Additional notes:
This standard was proposed by the Ministry of Machinery Industry of the People's Republic of China and is under the jurisdiction of the Standardization Research Institute of the Ministry of Machinery Industry. This standard was drafted by the Standardization Research Institute of the Ministry of Machinery Industry.
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