GB/T 197-2018 English PDF (GBT197-2018)

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GB/T 197-2018: General purpose metric screw threads -- Tolerances
GB/T 197-2018
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 21.040.10
J 04
Replacing GB/T 197-2003
General purpose metric screw threads - Tolerances
(ISO 965-1:2013, ISO general purpose metric screw threads -
Tolerances - Part 1: Principles and basic data, MOD)
ISSUED ON: MARCH 15, 2018
IMPLEMENTED ON: OCTOBER 01, 2018
Issued by: General Administration of Quality Supervision, Inspection and
Quarantine of the PRC;
Standardization Administration of the PRC.
Table of Contents
Foreword ... 3 
1 Scope ... 5 
2 Normative references ... 5 
3 Terms, definitions and symbols ... 5 
4 Tolerance system ... 7 
5 Tolerance positions ... 7 
6 Tolerance grades ... 9 
7 Lengths of engagement ... 12 
8 Recommended tolerance classes ... 18 
9 Tolerances of multiple-start threads ... 20 
10 Tolerance formulae ... 20 
11 Root contours ... 23 
12 Thread designation ... 25 
Annex A (Informative) Supplementary method for marking tolerance class of
coated threads ... 30 
Bibliography ... 32 
Foreword
"General purpose metric screw threads" has issued the following standards:
- GB/T 192-2003 General purpose metric screw threads - Basic profile;
- GB/T 193-2003 General purpose metric screw threads - General plan;
- GB/T 196-2003 General purpose metric screw threads - Basic dimensions;
- GB/T 197-2018 General purpose metric screw threads - Tolerances;
- GB/T 2516-2003 General purpose metric screw threads - Limit deviations;
- GB/T 9144-2003 General purpose metric screw threads - Preferable plan;
- GB/T 9145-2003 General purpose metric screw threads - Limits of sizes for
the screw threads of medium quality and preferable plan;
- GB/T 15756-2008 General purpose metric screw threads - Limits of sizes.
This Standard is the tolerance standard of "General purpose metric screw
threads".
This Standard is drafted in accordance with the rules given in GB/T 1.1-2009.
This Standard replaces GB/T 197-2003 "General purpose metric screw threads
- Tolerances".
Compared with GB/T 197-2003, the main technical changes of this Standard
are as follows:
- ADD four kinds of external thread tolerance positions (a, b, c and d) (see
Clause 5);
- ADD tolerances of multiple-start threads (see Clause 9);
- ADD the designation of coated threads (see 12.5 and Annex A);
- ADD the content of tolerance system (see Clause 4).
This Standard uses the redraft law to modify and adopt ISO 965-1:2013 "ISO
general purpose metric screw threads - Tolerances - Part 1: Principles and basic
data". The main technical differences between this Standard and ISO 965-
1:2013 and their reasons are as follows:
- As for the normative references, this Standard has made adjustments with
technical differences, to adapt to the technical conditions of China. The
adjustments are mainly reflected in Clause 2 “Normative references”. The
specific adjustments are as follows:
 Replace ISO 68-1 with GB/T 192, which modifies and adopts the
international standard;
 Replace ISO 261 with GB/T 193, which modifies and adopts the
international standard;
 Replace ISO 1502 with GB/T 3934, which modifies and adopts the
international standard;
 Replace ISO 5048 with GB/T 14791, which is identical to the
international standard.
- This Standard adds the designation of coated threads; expands the
applicable types of coated threads in the ISO standard; and avoids
misunderstandings about coated thread designation (see 12.5 and Annex
A).
- Delete Figure 1 of the ISO standard. The knowledge of limit deviation and
tolerance class has been popularized; there is no need to explain.
This Standard also makes the following editorial changes:
- Modify the standard name;
- ADD an informative Annex A.
This Standard was proposed by and shall be under the jurisdiction of National
Technical Committee 108 on Thread of Standardization Administration of China
(SAC/TC 108).
Drafting organizations of this Standard: Qifeng Precision Industry Sci-Tech
Corp., China Productivity Center for Machinery, Beijing Automotive Technology
Center Co., Ltd., Zhejiang Mekol Tools Co., Ltd., Zhejiang Changhua Auto Parts
Co., Ltd.
Main drafters of this Standard: Chen Yuezhong, Li Xiaobin, Luan Jianxin, Chen
Pengyu, Zhang Yiwei.
The previous editions of the standard replaced by this Standard were released
as follows:
- GB/T 197-1963, GB/T 197-1981, GB/T 197-2003.
General purpose metric screw threads - Tolerances
1 Scope
This Standard specifies the tolerances and designations of general purpose
metric screw threads. The basic profile and general plan of general purpose
metric screw threads shall meet the requirements of GB/T 192 and GB/T 193,
respectively.
This Standard applies to general purpose fastening threads.
2 Normative references
The following documents are indispensable for the application of this document.
For the dated references, only the editions with the dates indicated are
applicable to this document. For the undated references, the latest edition
(including all the amendments) are applicable to this document.
GB/T 192 General purpose metric screw threads - Basic profile (GB/T 192-
2003, ISO 68-1:1998, MOD)
GB/T 193 General purpose metric screw threads - General plan (GB/T 193-
2003, ISO 261:1998, MOD)
GB/T 3934 Specification of gauges for general purpose screw threads (GB/T
3934-2003, ISO 1502:1996, MOD)
GB/T 14791 Screw threads - Vocabulary (GB/T 14791-2013, ISO 5408:2009,
IDT)
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T
14791 apply.
3.2 Symbols
For the purposes of this document, the following symbols apply.
D - basic major diameter of internal thread (nominal diameter);
D1 - basic minor diameter of internal thread;
D2 - basic pitch diameter of internal thread;
d - basic major diameter of external thread (nominal diameter);
d1 - basic minor diameter of external thread (on the basic profile);
d2 - basic pitch diameter of external thread;
d3 - root minor diameter of external thread (on the design profile, see Figure
5);
P - pitch;
Ph - lead;
H - height of fundamental triangle;
S - “short” engagement length group;
N - “normal” engagement length group;
L - “long” engagement length group;
T - tolerance;
TD1 - tolerance for minor diameter of internal thread;
TD2 - tolerance for pitch diameter of internal thread;
Td - tolerance for major diameter of external thread;
Td2 - tolerance for pitch diameter of external thread;
EI - lower limit deviation of diameter of internal thread (fundamental
deviation);
ei - lower limit deviation of diameter of external thread;
ES - upper limit deviation of diameter of internal thread;
es - upper limit deviation of diameter of external thread (fundamental
deviation);
R - root radius of external thread (see Figure 5);
C - root truncation of external thread (see Figure 5).