Pipe threads for tubes andfittingswhere pressure-tight joints arenotmadeonthe threads (metric dimensions)
Committeesresponsibleforthis BritishStandard
This British Standard was entrusted by the Piping Systems ComponentsStandards Committee (PSE/-) to Technical Committee PSE/9 upon which the following bodies were represented:
Association of Hydraulic Equipment ManufacturersBritish Compressed Air SocietyBritish Engine Group of the Society of Motor Manufaeturers and Traders British Gas CorporationBritish Hydromechanics Research AssociationBritish Malleable Tube Fittings AssociationBritish Steel Industry British Valve Manufacturers Association Ltd.Copper Tube Fittings Manufacturers’ AssociationDepartment of Trade and Industry (National Engineering Laboratory)Engineering Equipment and Materials Users’ Association Energy Industries CouncilGauge and Tool Makers' AssociationInstitution of Civil Engineers Institution of Gas EngineersInstitution of Public Health EngineersInstitution of Water Engineers and ScientistsWater Authorities Association Water Companies AssociationWrought Fitting Makers’ Association
been prepared under the This British Standard havingdirection of the Piping Systems Components StandardsCommittee was published under the authority of the Board of BSI and es29 August 1986 into effect on
0 BSI 12-1998
Amendments issued since publication
First publisbed Deoember 1956First revision April 1973 Second revision August 1986
Amd. No. Date of issue Comments
The following BSI referenoesrelate to the work on this standard:Committee reference PSE/9 Draft for ment 85/75381 DC
ISBN 0 580 15212 X
Contents
PageCommittees responsible Foreword Inside front cover i1 Scope 12 Symbols 13 4 Classification and designation Thread details 1 4Appendix A Special truncated form of the Whitworththread for class A external threads Appendix B Notes on tolerancing system structure 5 5form by means of limit gauges Appendix C Method of verification of thread size andAppendix D Gauges for the method given in appendix C 6 8Figure 1 - Thread profile and tolerance zones 4Figure 2 - Special truncated external thread Figure 3 - NOT GO screw calliper gauge 5 7Figure 4 - Start of plete thread 8Figure 5 - Chamfer of start of thread Figure 6 - Thread profiles of Go ring gauges and 8their check plugs 6zones for Go ring gauges and their check plugs Figure 7 - Relative positions of pitch diameter tolerance 10Figure 8 Thread profles of Nor Go ring gauges and their check plugs and calliper gauges 11Figure 9 Relative positions of pitch diameter tolerance zonesfor NOT Go ring gauges calliper gauges and their check plugs Figure 10 - Thread profiles of Go and NOT GO plug gauges 12 13Figure 11 Relative positions of pitch diameter tolerance zonesfor CO and NOT GO plug gauges Table 1 - Basic dimensions and tolerances 14 3Table 2 - Special truncated fastening threads Table 3 - Dimensions for GO and NOr GO gauges and class A external threads 5their check plugs for class A external threads and for GO gauges and their check plugs for class B external threads 6Table 4 -- Other values for GO and NOT GO gauges andas a function of the pitch P their check plugs for class A and class B external threads 10Table 5 - Dimensions for NOT GO gauges and their 11Table 6 Dimensions for threaded GO and NoT Go plug gauges check plugs for class B external threads 13Table 7 - Other values for GO and NOT GO plug gauges as a function of the pitch P 14Publications referred to Inside back cover
Foreword
This revision of BS 2779 has been prepared under the direction of the PipingSystems Components Standards Committee. It supersedes BS 2779:1973 whichis withdrawn.
This standard is based on and is technically equivalent to the two Parts ofISO 228 *Pipe threads where pressure-tight joints are not made on the threads" namely ISO 228/1-1982 Designation dimensions and tolerances" andISO/2-1980 =Verification by means of limit gauges"; both Parts are published bythe International Organization for Standardization (ISO).
This standard provides a range of thread sizes which are considered to benecessary to fulfil general requirements. Dimensions are given in metric units only.
For ease of production it has been found convenient to reproduce the figures fromISO 228/2-1980 for Figure 4 Figure 5 Figure 7 Figure 10 and Figure 11 of this standard.
A British Standard does not purport to include allthe 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
Summary of pages
pages 1 to 14 an inside back cover and a back cover. This document prises a front cover an inside front cover pages i and i
This standerd has been updated (see copyright date) and may have hadamendments incorporated. This will be indicated in the amendment table on the inside front cover.
1 Scope
2 Symbols
Symbol Term
This British Standard specifies requirements for thefastening pipe threads having a thread size designation and dimensions of Whitworth formdesignation in the range 1/16 to 6 inclusive. Thispressure-tight joints are not made on the threads standard applies to pipe threads whereon the crests of the threads allows for truncation Dimensions are given in metric units. The tolerance(see 4.1).generally used fr fastening purposes such as the mehnical NOTE 1 The pipe threads covered by this standard areNOTE 2 The titles of the publications referred to in this assembly of the ponent parts of fittings cocks and valves ete.standard are listed on the inside back cover.
For the purposes of this British Standard thefollowing symbols apply.
b3 Width of clearance groove at the major and minor diameter of the thread profile withshortened flanks.d Basic major diameter of the external thread.d Basic minor diameter of the externald2 thread (d = d 1.280 654P). Basic pitch diameter of the external thread(d = d 0.640 327 P).D Basic major diameter of the internal thread (D = d).D Basic minor diameter of the internalD2 thread (D = D 1.280 654P = d). Basic pitch diameter of the internal thread(D = D 0.640 327P = d).h Height of the thread profile with roundedH Height of the triangle of the thread profile. crests and roots.m Distance between the middle of thetolerance zone Tp of the threaded ring gauge and the middle of the tolerance zoneTcp of the Go check plug.r p Radius of rounded crests and roots. Pitch.8 Displacement of the clearance groove with8 Tolerance on bg- shortened flanks.
Tolerance on the pitch diameter of Go andNOT Go threaded check plugs and wearra check plugs. Tolerance on the basic major diameter ofTaa the external thread.Tolerance on the basic pitch diameter of the external thread.p1 Tolerance on the basic minor diameter of the internal thread.Tp.2 Tolerance on the basic pitch diameter ofTpL. Tolerance on the pitch diameter of GO and the internal thread.NOT Go threaded plug gauges.TR NOT Go threaded ring gauges. Tolerance on the pitch diameter of GO andu A length equal to twice the radial height ofrounding at crest of root and thread (u = 0.147 84P).WGO Average amount available for thepermissible wear of Go threaded plug gauge and Go threaded ring gauge.WNG Average amount available for the permissible wear of NOr GO threaded pluggauge and NOT Go threaded ring gauge.ZpL. tolerance zone TpL of the Go threaded plug Distance between the middle of thegauge and the lower limit of the thread.ZR Distance between the middle of the tolerance zone Tg of the GO threaded ringgauge and the upper limit of the thread.
3 Classification and designation
3.1 Classes of external and internal threads
For internal threads one class of tolerance on the pitch diameter has been provided. For externalthreads two classes of tolerance on the pitchdiameter have been established as follows:
a) class A tolerance entirely negative valueequivalent to the internal thread tolerance (see Table 1);b) class B tolerance entirely negative value twicethat of the class A tolerance (see Table 1).
