ISOmetricscrew threads
Part2:Specificationforselectedlimitsof size
Cooperatingorganizations
The Mechanical Engineering Standards Committee under whose directionfollowing: this British Standard was prepared consist of representatives from the
Department of Trade (Marine Division)Department of Transport Electricity supply Industry in England andWalesEngineering Bquipment Users’ Association Federation of Manufacturers of ConstructionHealth and Safety Exeeutive Equipment and CranesInstitution of Gas EngineersInstitution of Plant Engineers Institution of Production EngineersLloyd's Rogister of Shipping London Transport ExecutiveMachine Tool Industry Research Asociation Ministry of Defence*National Coal Bonrd*Oil Companies Materials Association Process Plant AssociationRailway Industry Association of Great Britain* Society of Motor Manufacturers and TradersTelemunication Engineering and LimitedManufacturing Association (TEMA)*
Associated Offices Technical CommitteeAssociation of Hydraulic Equipment Association of Consulting EngineersManufaeturersAssociation of Mining Electrical and Mechanical EngineersBritish Compresed Air Society British Electrical and Allied ManufacturersAssociation (BEAMA)*British Gas Corporation British Gear Manufacturer' AssociationBritish Internal Combustion Engine Manufacturers’ Association*British Pump Manufacturers’ Association British Steel corporationBritish Steel IndustryCbmpe British Valve Manufactures' Association Ltd.Crown Agents for Oversea Govermments and Chartered Institution of Building ServicesDepartment of the Environment (PSA) AdministrationsDepartment of Industry (National Engineering Laboratory)
The Organization marked with an asterisk in the above list together with thefollowing were directly represented on this Technical Committee entrusted with the presentation of this British Standard:
Gauge and Tool Makers AssocintionScrew Thread Tool Manufacturers’ AssociationSociety of British Aerospace Companies LimitedIndividual manufacturer
Agricultural Engineers" AssociationBicycle Association of Great BritainBritish Industrial Fasteners Federation British Railways BoardBusines Equipment Trade Association Fasteners and Turmed Parts Institute
This British Standard having heen prepared under thedirection of the Mechanical Engineering Standards Committee was publishedExecutive Board and es under the authority of theinto effect on 31 December 1981
Amendments issued since publication
Amd. No Date of issue Comments5094 June 1986 Indicated by a sideline in the margin
C BSI 12-1998
First published June 1965Second revision December 1981 First revision December 1966
ISBN 0 580 12412 6
Contents
PageForeword Cooperating organizations Inside front cover ii1 Scope 12 Designation References 1Appendix A Additional tolerance classes for aerospace use 3 38 1Table 1 - ISO metric screw threads: limits and tolerances for finisheduncoated threads for normal length of engagement Table 2 ISO metric screw threads: limits and tolerances for finished 2uncoated threads for normal length of engagement for aerospace use 39Publications referred to Inside back cover
Foreword
This British Standard has been prepared under the direction of the MechanicalEngineering Standards Committee. It supersedes BS 3643-2:1966 and BS 3643-3:1967 which are therefore withdrawn.
BS 3643-1 contains details of the basic thread profile general plan of standard diameter/pitch binations basie thread dimensions tolerance principles andbasic data from the latest ISO metric screw thread standards.
The previous edition of BS 3643-2 specified the limits and tolerances for coarse pitch series threads in the range 1 mm to 68 mm diameter. The previous editionof BS 3643-3 specified the limits and tolerances for fine (constant) pitch threadsin the range 1 mm to 300 mm diameter.
In both Parts 2 and 3 three classes of fit were given “close" “medium” and “free” the respective nut/bolt tolerance classes being 5H/4h 6H/6g and 7H/8g. The same tolerance classes have been used as the basis for this standard but in addition thetolerance class 4H is specified for pitches up to and including 0.45 mm to alignwith Part 1. The selection of nut/bolt tolerance classes rests with the designer based on the information given in Part 1.
This edition of Part 2 bines the information previously given in both Parts 2the limits and tolerances for ISO metric threads in the most convenient form.For further detailed information see BS 3643-1.
and 3 and is set out in a single table so as to present designers and users with
Pending the publication of a British Standard on coated threads which will bebased on ISO/DIS 4042 BS 3382 should be consulted for guidance.
A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application.
Compliance with a British Standard does not of itself confer immunityfrom legal obligations.
Summary of pages This document prises a front cover an inside front cover pages i and i
3 Designation
1 Scope
This Part of this British Standard specifies thefundamental deviations tolerances and limits of size for the tolerance classes 4H 5H 6H and 7H forexternal threads (bolts) where appropriate for: internal threads (nuts) and 4h 6g and 8g for
The plete designation for a screw thread shallprise a designation for the thread system and a designation for the thread tolerance class (see 4.3and 6.4 of BS 3643-1:1981).
coarse pitch series within the range 1 mmto 68 mm diameter;
fine pitch series within the range 1 mm to 33 mmdiameter;
constant pitch series within the range 8 mm to 300 mm diameter.
For certain diameter/pitch binations toleranceclass 4H for internal threads and tolerance classes 6h and 4g for external threads have beenincluded in appendix A primarily for aerospace use.
NOTE Attention is drawn to the faet that with the different screw thread forms available there is the possibility ofmismatch. It is the responsibility of the designer of the end product to ensure that this possibility is reduced to a minimum. For further information see PD 6494.
2References
The titles of the standards publications referred toin this standard are listed on the inside back cover.
