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GB / T 5796 “Metric Trapezoidal Screw Threads” consists of four parts:
——Part 1: Profiles;
——Part 2: Diameter and thread pitch series;
——Part 3: Basic dimension;
——Part 4: Tolerance.
This part is the Part 1of GB/T 5796.
This Part adopts ISO 2901: 1993 "ISO Basic Profile and Maximum Material Profiles of Metric System Metric Trapezoidal Screw Threads" (English edition) by revision. The main differences between these two are as:
——Content of Chapter 4, pragraph 1 of ISO standard is deleted in our National Standard. It describes the relationship between “basic profile" of screw thread and diameter basic size / fundamental deviation. There are technical mistakes in this paragraph of ISO. "Designed profile” of screw thread is the starting point of fundamental deviation. As for Metric trapezoidal screw threads, there are some difference between" designed profile" and “basic profile "in the bottom (bottom diameter) of teeth. The basic dimension of bottom diameter (d3 and D4) of the former one is in a difference of 2ac (d1-d3=2ac; D4-D=2ac) respectively to the latter one. Besides, the bottom diameter dimension (d3 and D4) of the former has value in use, while the latter one' bottom diameter dimension (d1 and D4) doesn’t has using value.
——ISO Standard is not able to explain the reason of the existence of difference respectively between bottom diameter d3 and D4 of “maximum entity profile", bottom diameter" d1 profile” and D. "2ac” has nothing to do with the fundamental deviation of “basic profile”, so use “basic profile” and fundamental deviation can not lead to two “maximum entity profiles". "2ac” is the skill differential and interrelation between” basic profile" and "designed profile".
——In Chapter 3, comparing to ISO, our National Standard have added code number (d3 and D4) of bottom diameter of "designed profile", code number(H4 and h3)of teeth height and code number (R1 and R2) of radius of chamfer circle, and have deleted code number (es) of fundamental deviation. In order to instruct designing personnel ,our National Standard indicate the corresponding relationship between code numbers of each diameter, " designed dental pattern" and " basic profile " in 3.2 (code number)
——In Chapter２, our national standard do not reference tolerance standard (ISO 2903) of Metric trapezoidal screw threads. Because this Part only specifies screw thread profile, and doesn't involve content of thread tolerance. Meanwhile, in order to unify terms in Standard, our National Standard has added terminology standard (GB/T 14791) of screw thread in quoted standard.
——In Chapter 7, comparing to ISO standard, our national standard has deleted formula (z, d3, d2, D2, D1, D4 and s) of indirect parameter of screw thread profile. These parameters haven’t appeared in Table 2 of this part.
This Part replaces GB/T 5796.1-1986 “Metric trapezoidal screw threads profile".
Comparing to GB/T 5796.1-1986 “metric trapezoidal screw threads profile", major technical changes of this part are as follows: term " maximum entity profile" in old standard is replaced by "designed profile", that is, two "maximum entity profile" figures in old standard are replaced by a "design profile" figure (Chapter2 of 1986 edition and Chapter 6 and Chapter 7 of this edition).
GB/T 5796 is one of the two standards of metric trapezoidal screw threads. The estimated structure and its corresponding international standard of two national standards, and its substituted national standard are listed in following:
A) GB/T 5796 "Metric trapezoidal screw threads"
——Part 1: profile (ISO 2901 replace GB/T 5796.1-1986);
——Part 2: diameter and thread pitch series (ISO 2902 replace GB/T 5796.2-1986):
GB/T 5796.1-2005
——Part 3: basic dimension (ISO 2904; replace GB/T 5796.3-1986);
——Part 4: tolerance (ISO 2903; replace GB/T 5796.4- 1986).
B) GB/T 12359-1990 “Limit size of metric trapezoidal screw threads"
This standard is proposed and under the jurisdiction of the National Standardization Technical Committee of Non-ferrous Metal.
This part was drafted by the Academy of Machinery Science & Technology.
Chief drafting staff: Li Xiaobin
The previous editions of the part are:
——GB 784-65;
——GB/T 5796.1-1986
Metric Trapezoidal Screw Threads - Part 1: Profiles
1 Scope
GB/T 5796 of this part specifies basic profile and design profile of metric trapezoidal screw threads.
This Part is applicable to general purpose mechanical driven and connection of fasten metric trapezoidal screw threads.
2 Normative References
The clauses in the following documents contain provisions which, through reference GB/T 5796 of this part, constitute provisions of this part. For dated reference, subsequent amendments to (excluding correction to), or revisions of, any of these publications do not apply. However, the parties whose enter into agreement according to this Part are encouraged to research whether the latest editions of these references are applied or not. For undated references, the latest edition of the reference document is applicable to this part.
GB/T 14791 screw thread terms (neq ISO 5408:1983)
3 Terms and code numbers
3.1 Terms
Terms and definitions specified by GB / T 14791 are applicable to this Part.
3.2 Code Numbers
D ——large diameter of internal thread on basic profile;
D4 ——large diameter of internal thread on designed profile;
D ——large diameter (nominal diameter) of external thread on basic profile and designed profile;
D2 ——pitch diameter of internal thread on designed profile and designed profile;
d2 ——pitch diameter of external thread on designed profile and designed profile;
D1 ——minor diameter of internal thread on designed profile and designed profile;
d1 ——minor diameter of external thread on basic profile;
d3 ——minor diameter of external thread on designed profile;
P ——thread pitch;
H ——original altitude of a triangle;
H1 ——teeth height of basic profile;
H4 ——teeth height of internal thread on designed profile;
h3 ——teeth height of external thread on design profile;
ac ——crest clearance;
R1 ——arc radius of crest chamfer of external thread;
R2 ——arc radius of chamfer of thread' root.
4 Basic Profile
Basic profile is showed in Figure 1. Heavy lines in the Figure represent basic profile.
5 Dimension of Basic Profile
Dimension of basic profile is showed in Table1.
