GB/T 197-2018General purpose metric screw threads -- Tolerances (English PDF)

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 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.

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)

3 Terms, definitions and symbols

For the purposes of this document, the terms and definitions given in GB/T

14791 apply.

4 Tolerance system

The tolerance system consists of tolerance grades and tolerance positions. The

tolerance grades are expressed by number, such as 4, 6 and 8.The tolerance

positions are expressed by letter, such as H, G, h and g.

5 Tolerance positions

The following tolerance positions for internal and external threads are

standardized.

6 Tolerance grades

The tolerance grades for the following screw thread pitch and crest diameters

are standardized.

7 Lengths of engagement

The lengths of thread engagement are classified into three groups. short (S),

8 Recommended tolerance classes

In order to reduce the number of gauges and tools, the tolerance classes should

preferably be chosen from Tables 7 and 8.

9 Tolerances of multiple-start threads

With the same pitch, the crest diameter tolerances for multiple-start threads are

the same as for single-start threads.

10 Tolerance formulae

In order to give a uniform series of tolerance values, the above-mentioned

rounding principle is not completely followed.

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