Specificationfor
ISOmetric screw threads
Part1:Principlesandbasicdata
Cooperatingorganizations
The Mechanical Engineering Standards Committee under whose directionfollowing: this British Standard was prepared consists of representatives from the
Associated Offices Technical CommitteeAssociation of Consulting EngineersAssociation of Hydraulic Equipment ManufacturersAssociation of Mining Electrical and Mechanical EngineersBritish Compressed Air SocietyBritish Electrical and Allied Manufacturers Association (BEAMA)*British Gas Corporation British Gear Manufacturers’ AssociationBritish Internal Combustion EngineBritish Pump Manufacturers’ Association Manufacturers" Association*British Stoel Corporation British Steel IndustryBritish Valve Manufacturers' Association Ltd.Cbmpe Chartered Institution of Building ServicesCrown Agents for Oversea Governments and AdministrationsDepartment of the Environment (PSA)Department of Industry (Mechanical Engineering)Department of Industry (National Engineering Laboratoryj*
The organizations marked with an asterisk in the above list together with the following were directly represented on the Technical Committee entrustedwith the preparation of this British Standard:
Gauge and Tool Makers' Associntione po p mg AsociationSociety of Britiah Aerospace Companies LimitedIndividual manufacturer
Agricultural Engineers’ AssociationBieycle Association of Great Britain British Industrial Fasteners FederationBusiness Equipment Trade Association British Railways BoardFasteners and Turmed Parts Institute
This British Standard having been prepared under theEngineering Standards direetion of the MechanicalCommittee was published under the authority of theExecutive Board and es into effect on31 March 1981
Amendments issued since publication
BSI 02-1999
Date of issue Comments0168 May December Indicated by a sideline in the margin1984
Amd. No.
First publisbed June 1963First revision March 1981
The following BSI referenoesrelate to the work on this standard:Draft for ment 78/80250 DC Committee reference MEE/1
ISBN 0 580 11626 3
Contents
PageCooperating organizations Foreword Inside front cover i1 Seope 12 References Basic profile 13 4 General plan 1 25 Tolerances: principles and basic data Basic dimensions 96 7 Tolerances: deviations for constructional threads 29 14Appendix A Notes for guidance 47Appendix B Outline guide and examples for caleulating limits of size of untabulated metric screw threads 49Figure 1 - Basic profile of ISO metric thread 1Figure 3 - Tolerance positions with respect to zero line Figure 2 - Basic dimensions 9(basic size) Figure 4 - Nut threads with tolerance position G 15 17Figure 5 - Nut threads with tolerance position H 17Figure 6 - Bolt threads with tolerance positions e f and g 18Figure 8 - Bolt root profile Figure 7 - Bolt threads with tolerance position h 96 18Figure 9 - Maximum material profiles for internal and external threads 47Table 1 - Basic profile dimensions 2Table 2- Maximum diameters Table 3 - Diameter/pitch binations 3Table 4 - Basic dimensions 4 7Table 5 Fundamental deviations for nut threads and bolt threads 19Table 6 - Lengths of thread engagement 0Table 7 - Minor diameter tolerances of nut thread (TD ) Table 81 Major diameter tolerance of bolt thread (T) 21 22Table 9 - Pitch diameter tolerance of nut thread (Tp) 23Table 10- Table 11 -- Pitch diameter toleranee of bolt thread (7) Minimum root radi 24 25Table 12 -- Tolerance classes for nuts 97Table 14 - Deviations Table 13 - Tolerance classes for bolts 28Publications referred to Inside back cover
Foreword
This revised British Standard has been prepared under the direction of theMechanical Engineering Standards Committee. It is based on the following ISO standards relating to ISO metric screw threads prepared by Technical CommitteeISO/TC 1 Screw threads of the International Organization for Standardization (ISO). The clauses in this standard have been so arranged that each relatesdirectly to the relevant ISO standard as indicated:
Clause 4: ISO 261-1973 Clause 3: ISO 68-1963Clause 5: ISO 724-1968Clause 6: ISO 965/1-1980Clause 7: ISO 965/3-1980
ISO 965/2-1973 “ISO general purpose metric screrw threads -TolerancesPart II Limits of sizes for mercial bolt andnut threadsMedium quality has not been included as a separate clause in this standard as the limits of sizeslisted are specified in BS 3643-2.
ISO 965 has been revised by ISO/TC 1 to include the tolerance position “f' and the modified bolt root profile. This information has been included in this standard.
Serew thread terms and definitions can be found in BS 6528 (identical withISO 5408-1983) and these will be adopted in future standards and revised existing standards.
Some terms used in this standard based on the established ISO standards may be at variance with or do not appear in BS 6528; e.g. “crest diameter” is used inclause 6 but is not defined in BS 6528. However it has been decided to leave thisdescriptive term which is used to embrace the terms “major diameter of bolt thread” and “minor diameter of nut thread". Moreover the term “nominal size or“nominal diameter is often confused with basic size whereas it is now defined in BS 6528 as “The size which is used for the purpose of general identification. It is generally the basic major diameter of the thread".
ISO 262 “ISO general purpose metric serew threads -Selected sizes for screws
bolts and nuts has not been included as a separate clause in this standard asthose sizes will be specified in the various produet standards. However its contents form part of Table 3 in clause 4.
In order to establish a recognized fine series a selection of diameter/pitchbinations has been taken from ISO 261. For nominal diameters up to and(other than the coarse pitch) and therefore these pitches have been included in this standard. The pitches for nominal diameters larger than M7 have beenextracted from ISO 262.
The information given in Appendix A has been given in this form rather than in
the appropriate clauses in the standard so that each clause maintains as far aspossible the ISO format to enable direct cross reference with the ISO standards and the standards of other countries that are also based on the ISO standards.
The information given in Appendix B for the calculation of limits of size for screwthreads recognizes that the limitations of the ISO standards on nominal sizes i.e. 1.0 mm (minimum) to 300 mm (maximum) diameters and also the
diameter/pitch binations may at times need to be exceeded.
requirements of BS 3643 it is permissible for them to be manufactured to the MJ When serew threads for aerospace purposes are specified to ply with theroot radius of that profile. Attention is drawn to the fact that the MJ threads profile in BS 6293 and for their limits of size to be modified accordingly to suit thespecified in BS 6293 is the preferred series for aerospace use.
Terminology and conventions. For ease of production it has been found convenient to reproduce the tables of the international standards withnot identical with those used in British Standards; attention is especially drawn amendments where necessary. Some terminology and certain conventions areto the following.
The ma has been used throughout as a decimal marker. In British Standards it is current practice to use a full point on the baseline as the decimal marker.A British Standard does not purport to include all the necessary provisions of acontract. Users of British Standards are responsible for their correct application.
from legal obligations. Compliance with a British Standard does not of itself confer immunity
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