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This document is drafted in accordance with the rules given in GB/T 1.1-2020 Directives for standardization - Part 1: Rules for the structure and drafting of standardizing documents.
This document is Part 1 of GB/T 5796 Trapezoidal screw threads. The following parts of GB/T 5796 have been published:
——Part 1: Profiles;
——Part 2: General plan;
——Part 3: Basic dimensions;
——Part 4: Tolerances.
This document replaces GB/T 5796.1-2005 Trapezoidal screw threads - Part 1: Profiles. In addition to structural adjustment and editorial changes, the following main technical changes have been made with respect to GB/T 5796.1-2005:
——The symbol of the thread height on basic profile is changed from “H1” to “H2” (see Clause 4; 3.2 in Edition 2005);
——The symbols of the thread overlap on design profile “H0” and the width of flat crest or root on basic profile “w” are added (see Clause 4);
——The description on the starting positions of thread limit deviations is added (see Clause 6);
——The number of decimal places of coefficients is changed from 3 to 9 in the calculation formula for the fundamental triangle height H (see Clause 5; Table 1 in Edition 2005).
This document is modified in relation to ISO 2901:2016 ISO metric trapezoidal screw threads – Basic and design profiles.
The technical differences with respect to ISO 2901:2016 and their justifications are as follows:
——The standard ISO 5408 is changed from information to normative reference, and replaced by GB/T 14791 (see Clause 3), so as to make it meet the compilation requirements for national standards;
——The tips in Tables 1 and 2 are changed from statements to requirements (see Clauses 5 and 6), and the attributes of the requirements in the two tables are clarified;
——The basic dimension formulae for major, pitch and minor diameters of thread (D1, d2 and D2, d3, D4) are deleted (see Clause 6 in ISO 2901:2016), without repeating the corresponding technical content given in GB/T 5796.3.
The following editorial changes have been made in this document:
——The name of the document is changed to Trapezoidal screw threads - Part 1: Profiles.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. The issuing body of this document shall not be held responsible for identifying any or all such patent rights.
This document was proposed by and is under the jurisdiction of SAC/TC 108 National Technical Committee on Screw Threads of Standardization Administration of China.
This document was firstly issued in 1965, firstly revised in 1986, secondly in 2005, and thirdly this time.
Introduction
GB/T 5796 Trapezoidal screw threads consists of four parts.
——Part 1: Profiles. It provides a technical basis for establishing the basic dimension formulae for thread diameters and determining the starting positions for thread tolerance zone in Parts 3 and 4.
——Part 2: General plan; It provides a specification basis for nominal diameters and pitches to establish the basic dimension table for thread diameters and determine the thread tolerance table in Parts 3 and 4.
——Part 3: Basic dimensions. It provides a technical basis for determining the limit size of thread diameter.
——Part 4: Tolerances. It provides a technical basis for production and inspection of the products.
Profiles, general plan, basic dimensions and tolerances constitute a complete system of technical parameters for Trapezoidal screw threads. These technical parameters are specified as a single standard to be convenient for users to check and use.
Trapezoidal screw threads - Part 1: Profiles
1 Scope
This document specifies the basic and design profiles of trapezoidal screw threads.
This document is chiefly applicable to traversing threads for traversing motion on machines, tools, etc. It may also be used for fastening threads.
2 Normative references
The following documents contain provisions which, through reference in this text, constitute provisions of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 14791 Screw threads - Vocabulary (GB/T 14791-2013, ISO 5408:2009, IDT)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 14791 apply.
4 Symbols
For the purposes of this document, the following symbols apply.
D major diameter of internal thread on basic profile (nominal diameter)
D4 major diameter of internal thread on design profile
d major diameter of external thread (nominal diameter)
D2 pitch diameter of internal thread
d2 pitch diameter of external thread
D1 minor diameter of internal thread
d1 minor diameter of external thread on basic profile
d3 minor diameter of external thread on design profile
P pitch
H fundamental triangle height
H2 thread height on basic profile
H0 thread overlap on design profile
H4 thread height of internal thread on design profile
h3 thread height of external thread on design profile
ac clearances at major and minor diameters on design profile
w width of flat crest or root on basic profile
R1 radius on crest corners of external thread on design profile
R2 radius on root corners of internal and external threads on design profile
5 Basic profile
The basic profile is shown as a thick line in Figure 1. It is common to internal and external threads.
The dimensions of the basic profile are given in Table 1. The dimensions of the basic profile are calculated by using the following formulae:
Foreword II
Introduction IV
1 Scope
2 Normative references
3 Terms and definitions
4 Symbols
5 Basic profile
6 Design profile
