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Hexagon Socket Countersunk Head Screws · GB/T 70.3-2023
Socket Head Screws

Hexagon Socket Countersunk Head Screws

GB/T 70.3-2023 (reference only)

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GB/T 70.3-2023 dimension drawing

Dimensions in mm
GB/T 70.3-2023 dimension drawing

Specification parameters

Technical conditions and referenced standards
Steel Stainless steel
General technical requirements
  • GB/T 16938
Thread
Tolerances
  • 6g
Standard
  • GB/T 197
Mechanical properties
Property class
  • Property classes 8.8, 10.9 and 12.9 b
  • A2-50, A4-50;
  • A2-70, A4-70;
  • A2-80, A4-80
Standard
  • GB/T 3098.1c
  • GB/T 3098.6c
Designation
  • 08.8, 010.9, 012.9
  • A2-050, A4-050
    A2-070, A4-070
    A2-080, A4-080d
Tolerances
Product grade
  • A
Standard
  • GB/T 3103.1
Surface treatment
  • No treatment (uncoated and unplated) ;
  • Electroplating requirements in accordance with GB/T 5267.1;
  • Non-electrolytically applied zinc flake coating requirements in accordance with GB/T 5267.2
  • Simple treatment (cleaning and polishing) ;
  • Passivation e
Any other technical requirements or surface treatments shall be agreed between the purchaser and supplier.
Surface discontinuities
  • GB/T 5779.1: Property classes 8.8 and 10.9;
  • GB/T 5779.3f: Property class 12.9
  • –
Acceptance inspection and packaging
  • GB/T 90.1, GB/T 90.2
  • a Depending on the coating type, the thread tolerance position for uncoated fasteners may be specified in accordance with the relevant coating standard. ;
  • b Fasteners of property class 12.9 are susceptible to hydrogen embrittlement. See GB/T 3098.1 and GB/Z 41117 ;
  • c See Table 5 for the minimum tensile loads for screws with reduced loadability;
  • d If the thread length of a fully threaded screw is too short for tensile testing in accordance with GB/T 3098.6, its designation shall include only the stainless steel group and omit the property class. ;
  • e  GB/T 5267.4 specifies passivation methods ;
  • f By agreement between the purchaser and supplier, this may also apply to property classes 8.8 and 10.9.

Product overview

An internal hex drive and a countersunk head for flush seating in a matching recess. This standard covers screws with reduced loadability.

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