This part specifies the cross recessed hexagonal head self-tapping screw and flat washer assembly with self-tapping thread specifications of ST2.9 to ST8, flat bearing surface, and mechanical properties in accordance with GB/T3098.5. The washer in the assembly should be able to rotate freely without falling off. GB/T 9074.20-2004 Cross recessed hexagonal head self-tapping screw and flat washer assembly GB/T9074.20-2004 Standard download decompression password: www.bzxz.net

ICS 21. 060. 10
National Standard of the People's Republic of China
GB/T 9074.20-—2004
Replaces GB/T 9074.20—1988
GB/T 9074.21—1988
Cross recessed hexagon head tapping screw with indentation andwasher assemblies with plain washersPromulgated on 2004-02-10
General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of ChinaAdministration of Standardization of the People's Republic of China
Implementation on 2004-08-01
This part is one of the national standard "Fasteners-Assemblies" product series standards. This series includes: GB/T9074.1-2002 bolt or screw and flat washer assembly; a)
GB/T 9074.2-1988
cross recessed pan head screw and external serrated lock washer assembly; GB/T 9074.3-1988
cross recessed pan head screw and spring washer assembly: c)
GB/T 9074. 4---1988wwW.bzxz.Net
cross recessed pan head screw, spring washer and flat washer assembly; GB/T9074.5-2004 cross recessed small pan head screw and flat washer assembly; e)
GB/T 9074. 7-1988
cross recessed small pan head screw and spring washer assembly; GB/T 9074. 8—1988
Cross recessed small pan head screw, spring washer and flat washer assembly; GB/T 9074.9—1988
Cross recessed countersunk head screw and tapered locking washer assembly; i) GB/T 9074.10--1988
Cross recessed semi-countersunk head screw and tapered locking washer assembly; GB/T 9074.11-—1988
Cross recessed hexagon head bolt and flat washer assembly; GB/T 9074. 12--1988
Cross recessed hexagon head bolt and spring washer assembly; GB/T 9074.20—2004
GB/T 9074.13—1988
3 Cross recessed hexagonal head bolt, spring washer and flat washer assembly; 1)
GB/T9074.15--1988 Hexagonal head bolt and spring washer assembly; GB/T9074.16-1988 Hexagonal head bolt and external serrated lock washer assembly; GB/T9074.17-1988 Hexagonal head bolt, spring washer and flat washer assembly; GB/T 9074.18-2002
Self tapping screw and flat washer assembly;
GB/T9074.20-2004, Cross recessed hexagonal head self tapping screw and flat washer assembly. g)
This part is part 20 of GB/T9074. This part replaces GB/T9074.20-1988 "Cross recessed hexagonal head tapping screw and flat washer assembly" and GB/T9074.21-1988 "Cross recessed hexagonal head tapping screw and large washer assembly". Compared with GB/T9074.20-1988 and GB/T9074.21-1988, the main changes of this part are as follows: the two old standards are merged into one standard; two types of washers are given for selection (see Table 1); the hardness range of washers is specified, and measures should be provided to prevent hardness changes during heat treatment after assembly (see Table 2); the codes of tapping screws and washers for assemblies are added (see Table 3); and a new marking method for assemblies is specified (see Chapter 5). This part is proposed by the China Machinery Industry Federation. This part is under the jurisdiction of the National Technical Committee for Standardization of Fasteners (SAC/TC85). This part is drafted by the Mechanical Science Research Institute. The previous versions of the standards replaced by this part are: GB/T 9074.20—1988;
-GB/T 9074. 21--1988.
1 Scope
Cross recessed hexagonal head self-tapping screw
Flat washer assembly
GB/T9074.20—2004
This part specifies the cross recessed hexagonal head self-tapping screw and flat washer assembly with self-tapping thread specifications of ST2.9 to ST8, flat bearing surface, and mechanical properties in accordance with GB/T3098.5. The washers in this assembly should be able to rotate freely without falling off. 2 Normative references
The provisions in the following documents become the provisions of this part through reference to this part of GB/T9074. For dated references, all subsequent amendments (excluding errata or revisions) are not applicable to this part. However, parties to agreements based on this part are encouraged to study whether the latest versions of these documents can be used. For undated references, the latest versions apply to this part.
GB/T90.1 Fastener acceptance inspection (GB/T90.1—2002, idtISO3269:2000) GB/T90.2 Fastener marking and Packaging
GB/T97.5 Flat washers for self-tapping screws and washer assemblies (GB/T97.5—2002eqvISO10669:1999)GB/T1237 Fastener marking method (GB/T1237-2000, eqvISO8991:1986)GB/T3098.5 Mechanical properties of fasteners Self-tapping screws (GB/T3098.5--2000, idtISO2702:1992)GB/T 5267.1 Fastener plating (GB/T5267.1-2002, ISO4042:1999, IDT) GB/T9456 Cross recessed hexagonal head tapping screws 3 Dimensions
3.1 The dimensions of the tapping screws (see Figure 1) in the assembly shall comply with the provisions of GB/T9456 except for the parts where the washers are assembled, which shall comply with the following requirements:
The screws shall have a thin rod with a diameter of d. (see Figure 2), and the diameter of the washers shall comply with GB/T 97.5, so that it can rotate freely. The distance from the bearing surface to the beginning of the first thread should be increased to accommodate the maximum thickness of the washer. The transition circle diameter d (see Figure 2 and Table 1) should be less than the transition circle diameter d specified in GB/T9456, and the reduction is the difference between the nominal diameter and the rough diameter of the rolled thread. 3.2 The dimensions of the flat washer shall be in accordance with GB/T97.5. Field
Figure 1 Example 1 of cross recessed hexagonal head tapping screw and flat washer assembly
GB/T 9074.20—2004
Thread specifications
Transition circle diameter d. and shank diameter ds
Table 1 Dimensions
Standard series
Flat washers dimensions·
a Dimensions extracted from GB/T97.5 are for information only. b Dimension a is measured after the washer contacts the screw bearing surface or the fillet under the head. Technical conditions and referenced standards
Technical conditions and referenced standards are shown in Table 2.
Table 2 Technical conditions and referenced standards
Mechanical properties
Surface treatment
Acceptance and packaging
Self-tapping screws
GB/T 3098. 5
Unit: mm
Major series
GB/T 97. 5
Galvanizing technical requirements, according to GB/T5267.1
GB/T 90. 1, GB/T 90. 2
αIn order to avoid the influence on the hardness of the gasket during the heat treatment process, appropriate protective measures should be taken for the gasket before assembly, such as copper plating. Marking
5.1 The marking of the assembly should include the following: description of the component;
number of this national standard;
characteristics of self-tapping screws;
type code of self-tapping screws (see Table 3);
type code of washers (see Table 3).
Cross recess
Hexagon head tapping screw
Flat washer
For tapping screw and washer assembly
Table 3 Type code of tapping screw and washer
5.2 Marking method shall be in accordance with GB/T1237.
5.3: Marking example
Standard series
Major series
GB/T 9074.20—2004
Standard number
GB/T 9456
Cross recessed hexagon head tapping screw and flat washer assembly includes: one GB/T9456ST4.2×16, cone end (C) cross recessed hexagon head tapping screw (code S1) and one GB/T97.5 standard series washer (code N) assembly surface galvanized passivation (omitted mark) mark:
Self tapping screw and washer assembly GB/T9074.20ST4.2 X16S1N cross recessed hexagonal head self-tapping screw and flat washer assembly includes: a GB/T9456ST4.2×16, cone end (C) cross recessed hexagonal head self-tapping screw (code S1) and a GB/T97.5 large series washer (code L) assembly surface galvanized passivation (marks omitted:
self-tapping screw and washer assembly GB/T9074.20ST4.2X16S1L
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