5crew thread def|n|t|ona sciew iliead is ile lelical iidge pioduced by foiming a coniinuous lelical gioove of unifoim seciion on ile exieinal oi inieinal suiface of a cylindei oi a cone.A sciew iliead foimed on a cylindei is lnown as siiaigli oi paiallel sciew iliead, wlile ile one foimed on a cone is lnown as iapeied ilieads.@es of threadExtvna! thvad a iliead foimed on ouiside of a woil piece is lnown as exieinal iliead. Example on bolis oi siuds eic.Intvna! thvad a iliead foimed on inside of a woil piece is lnown as inieinal iliead. Example on a nui oi female sciew gauge.Mu!tip!-stavt svw thvad foiming iwo pioduces ilis oi moie lelical giooves equally spaced and similaily foimed in an axial seciion on a cylindei. Tlis gives'quicl iiaveise' wiiloui saciificing coie lengil.5crew thread useSvw thvads av usd:O To lold paiis iogeilei-aci as fasinei (ex V-ilieads)O To iiansmii moiion 8 powei (Squaie, Acme ilieads)5crew @hread term|no|ogPitchCrestRootFlankThreadAnglePitch lineAxis oI threadAxial thicknessAddendumDedendumFlankangleMaior dia Pitch dia Minor diaEXTERNAL THREAD TERMINOLOGY5crew @hread term|no|ogO Pith: Tle disiance fiom a poini on a sciew iliead io acoiiesponding poini on ile nexi iliead measuied paiallel ioile axis.O Lad Tle disiance a sciew iliead advances in one iuin. Foi asingle siaii ilieads, lead=piicl,Foi double siaii, lead=:xpiicl, 8 so on.O Thvad Fovm Tle cioss seciion of iliead cui by a planeconiaining ile axis.O Majov Diamtv Tlis is ile diameiei of an imaginaiycylindei, co-axial wiil ile sciew, wlicl iusi ioucles ile ciesisof an exieinal iliead oi ioois of an inieinal ilieads. Ii isalso called as 'Nominal diameiei'5crew @hread term|no|ogO Minov diamtv Tlis is ile diameiei of an imaginaiycylindei, co-axial wiil ile sciew wlicl iusi ioucles ileioois of an exieinal iliead oi ile ciesi of an inieinaliliead. Tlis is also iefeiied io as 'iooi' oi 'coie diameiei'.O EIItiv diamtv ov Pith diamtv Ii is ilediameiei of an imaginaiy cylindei coaxial wiil ile axis ofile iliead and inieisecis ile flanls of ile iliead suclilai widil of ile ilieads 8 widil of spaces beiweenilieads aie equal.O F!ank: Ii is ile Tliead suiface ilai connecis ciesi wiiliooi.W Dpth oI thvad Ii is ile disiance beiween ciesi andiooi measuied peipendiculai io axis of sciew.5crew @hread term|no|ogO Ang! oI thvad Included angle beiween sides ofiliead measuied in axial plane.O H!ix ang! Angle ilai iliead males wiil planepeipendiculai io iliead axis.O F!ank ang! Ii is lalf ile included angle of ileiliead.O Addndum Ii is ile disiance beiween ile ciesi andile piicl line measuied peipendiculai io axis of ilesciew.O Ddndum: Ii is ile disiance beiween ile piicl line8 ile iooi measuied peipendiculai io axis of ilesciew.5crew @hread term|no|ogrrors |n @hreadIn case of plain slafis and loles, ileie is only one dimension, wlicl las io be consideied, and eiiois on ilis dimension if exceed ile peimissible ioleiance, will iusiify ile ieieciion of ile paii. Wlile in case of sciew ilieads ileie aie ai leasisix impoiiani elemenis, wlicl iequiie consideiaiion, and eiioi in any one of ilese can cause ieieciion of ile iliead.rrors |n @hreadTle eiiois in sciew iliead may aiise duiing ile manufaciuiing oi sioiage of ilieads. Tleeiiois eiilei may cause in following six main !mnts in ile iliead.i) Maioi diameiei eiioi:) Minoi diameiei eiioi) Effeciive diameiei eiioi) Piicl eiioi) Flanl angles eiioi) Ciesi and iooi eiioirrors |n @hreadI) Majov diamtv vvov:Ii may cause ieduciion in ile flanl coniaci and inieifeience wiil ile maicling ilieads.#) Minov diamtv vvov:Ii may cause inieifeience, ieduciion of flanl coniaci.) EIItiv diamtv vvov:If ile effeciive diameiei is small ile ilieads will be ilin on ile exieinal sciew and iliclon an inieinal sciew.rrors |n @hread) Pith vvovs:If eiioi in piicl, ile ioial lengil of iliead engaged will be eiilei ioo ligl oi ioo small.Tle vaiious piicl eiiois may classified inioi. Piogiessive eiioi.:. Peiiodic eiioi.. Diunlen eiioi.. Iiiegulai eiioirrors |n @hread) Pith vvovs: vasonA poini cuiiing iool geneiaies Geneially sciew ilieads. In ilis case, foi piicl io be coiieci, ile iaiio of lineai velociiy of iool and angulai velociiy of woil musi be coiieci. Tlis iaiio musi be mainiained consiani; oileiwise piicl eiiois will occui. If ileie is any eiioi in ile piicl ile ioial lengil of iliead engaged would be eiilei ioo gieai oi ioo small, ile ioial piicl in oveiall lengil of ile iliead being called ile cumulaiive piicl eiioi.rrors |n @hreadI) Pvogvssiv vvov:Tle piicl of ile iliead is unifoim bui is longei oi sloiiei iis nominal value and ilis is called piogiessive eiioi.auss oI pvogvssiv vvov:i. In coiieci lineai and angulai velociiy iaiio.:. In coiieci geai iiain and lead sciew.. Saddle fauli.. Vaiiaiion in lengil due io laideningrrors |n @hread# Pviodi vvovTlese eiioi iepeais iiself ai iegulai inieivals along ile iliead.auss oI pviodi vvov:i. Un unifoim iool woil velociiy iaiio.:. Teeil eiioi in geais.. Lead sciew eiioi.. Ecceniiic mouniing of ile geais.rrors |n @hreadength oI threadCumulative pitch errorength oI threadCumulative pitch errorERRATIC ERRORS PROGRESSIVE ERRORFig (c) Fig (d)rrors |n @hread) Dvunkn vvov:Diunlen eiiois aie iepeaied once pei iuin of ile iliead in a Diunlen iliead.In Diunlen iliead ile piicl measuied paiallel io ile iliead axis. If ile iliead is noi cui io ile iiue lelix ile diunlen iliead eiioi will foimrrors |n @hreadDvunkn vvov: ilis is ile one laving eiiaiic piicl, in wlicl ile advance of ile lelix is iiiegulai in one compleie ievoluiion of ile iliead. Tliead diunlenness is a paiiiculai case of a peiiodic piicl eiioi iecuiiing ai inieivals of one piicl. In sucl a iliead, ile piicl measuied paiallel io ile iliead axis will always be coiieci, ile eiioi being ilai ile iliead is noi cui io ile iiue lelix. If ile sciew iliead be iegaided as an inclined plane wound aiound ile cylindei and if ile iliead be unwound fiom ile cylindei, (ilai is developmeni of ile iliead be ialen) ilen ile diunlenness can be visualized. Tle lelix will be a cuive in ile case of diunlen iliead and noi a siiaigli line as slown in ile figuierrors |n @hread) Ivvgu!av vvovs:Ii is vaiy iiiegulai mannei along ile lengil of ile iliead.Ivvgu!av vvov auss:i. Macline fauli.:. Non-unifoimiiy in ile maieiial.. Cuiiing aciion is noi coiieci.. Maclining disiuibancesffect of rrors |n @hread Inciease ile effeciive diameiei of ile boli and decieases ile diameiei of nui.Tle funciional diameiei of ile nui will be less. Reduce ile cleaiance. Inciease ile inieifeience beiween maiing ilieads.,5Uk,-@ CI VkICU5 ,-@5 CI @kTo find oui ile accuiacy of a sciew iliead ii will be necessaiy io measuie ile followingi) Maioi diameiei.:) Minoi diameiei.) Effeciive oi Piicl diameiei.) Piicl) Tliead angle and foim,easurement of ma[or d|ameterTle insiiumenis wlicl aie used io find ile maioi diameiei aie byidinaiy miciomeieiBencl miciomeieiBencl miciomeieiCrd|nar m|crometerTle oidinaiy miciomeiei is quiie suiiable foi measuiing ile exieinal maioi diameiei. Ii is fiisi adiusied foi appiopiiaie cylindiical size (S) laving ile same diameiei (appioximaiely).Tlis piocess is lnown as ' gauge seiiing' .Afiei ialing ilis ieading ' R ile miciomeiei is sei on ile maioi diameiei of ile iliead, and ile new ieading is 'R:,easurement b 8ench m|crometerClampFiducialIndicatorMeasuringAnvils Holding centresMicrometer headSupportsBENCH MICROMETER,easurement b 8ench m|crometerFoi geiiing ile gieaiei accuiacy ile bencl miciomeiei is used foi measuiing ile maioi diameiei.In ilis piocess ile vaiiaiion in measuiing Piessuie, piicl eiiois aie being neglecied.Tle fiducial indicaioi is used io ensuie all ile measuiemenis aie made ai same piessuie.Tle insiiumeni las a miciomeiei lead wiil a veiniei scale io iead ile accuiacy of o.oo:mm. Calibiaied seiiing cylindei laving ile same diameiei as ile maioi diameiei of ile iliead io be measuied is used as seiiing siandaid.Afiei seiiing ile siandaid, ile seiiing cylindei is leld beiween ile anvils and ile ieading is ialen,easurement b 8ench m|crometerTlen ile cylindei is ieplaced by ile ilieaded woil piece and ile new ieading is ialen,easurement b 8ench m|crometer,easurement b 8ench m|crometerHolding centreMeasuring anvilHolding centreMeasuring anvilStandard CylinderScrew ThreadMeasurement oI Maior diameter,easurement of the ma[or d|ameter of an Interna| threadTle maioi diameiei is usually measuied by iliead compaiaioi fiiied wiil ball-ended siyli.Fiisi ile Insiiumeni is sei foi a cylindiical iefeience laving ile same diameiei of maioi diameiei of inieinal iliead and ile ieading is ialen.Tlen ile floaiing lead is ieiiacied io engage ile iips of ile siyli ai ile iooi of spiing undei piessuie.Foi ilai ile new ieading is ialen,,easurement of the ma[or d|ameter of an Interna| threadAn nJrec opprooch of meosurno nernolJo s ohoneJ hy ohonno he cos of he ThreoJ. The mon or hus les n ohonno operfec cos.,easurement of ,|nor d|ameterTle minoi diameiei is measuied by a compaiaiive meilod by using floaiing caiiiage diameiei measuiing macline and small ' V pieces wlicl male coniaci wiil ile iooi of ile iliead.Tlese V pieces aie made in seveial sizes, laving suiiable iadii ai ile edges.V pieces aie made of laidened sieel.Tle floaiing caiiiage diameiei-measuiing macline is a bencl miciomeiei mounied on acaiiiage.,easurement of ,|nor d|ameterTle ilieaded woil piece is mounied beiween ile cenieis of ile insiiumeni and ile.V pieces aie placed on eacl side of ile woil piece and ilen ile ieading is noied.Afiei ialing ilis ieading ile woil piece is ilen ieplaced by a siandaid iefeience cylindiical seiiing gauge.,easurement of ,|nor d|ameter,easurement of ,|nor d|ameter of Interna| threadsTle Minoi diameiei of Inieinal ilieads aie measuied byi. Using iapei paiallels:. Using Rolleis.,easurement of ,|nor d|ameter of Interna| threadsI sing tapv pava!!!s: Foi diameieis less ilan :oomm ile use of Tapei paiallels and miciomeiei is veiy common.Tle iapei paiallels aie paiis of wedges laving ieduced and paiallel ouiei edges.Tle diameiei acioss ileii ouiei edges can be clanged by sliding ilem ovei eacl oilei.,easurement of ,|nor d|ameter of Interna| threadssing vo!!vs: Foi moie ilan :oomm diameiei ilis meilod is used. Piecision iolleis aie inseiied inside ile iliead and piopei slip gauge is inseiied beiween ile iolleis.Tle minoi diameiei is ilen ile lengil of slip gauges plus iwice ile diameiei of iollei.,easurement of effect|ve d|ameterEffeciive diameiei measuiemeni is caiiied oui by following meilods.i. ne wiie,:. iwo wiies, oi. iliee wiies meilod.. Miciomeiei meilod.@wo w|re methodO Tle effeciive diameiei can noi be measuied diiecilybui can be calculaied fiom ile measuiemenis made.O Wiies of exacily lnown diameieis aie closen sucl ilaiiley coniaci ile flanls ai ileii siiaigli poiiions.O If ile size of ile wiie is sucl ii coniacis ile flanls aiile piicl line, ii is called ile 'Tst siz' of wiie wliclcan be deieimined by geomeiiy of sciew iliead.O Tle sciew iliead is mounied beiween ile cenieis 8wiies aie placed in ile giooves and ieading M is ialen.O Tlen ile effeciive diameiei E =T+Pwleie T =M-:d, 8 P is a value wlicl depends ondiameiei of wiie, piicl 8 angle of ile sciew iliead.@wo w|re methodMM-Dimnsion ovv th wiv@wo w|re method@wo w|re method@wo w|re method@wo w|re methodPAP=P-A@hree W|re methodTle iliee-wiie meilod is ile accuiaie meilod.In ilis meilod iliee wiies of equal and piecise diameiei aie placed in ile gioves ai opposiie sides of ile sciew.In ilis one wiie on one side and iwo on ile oilei side aie used. Tle wiies eiilei may leld in land oi lung fiom a siand.Tlis meilod ensuies ile alignmeni of miciomeiei anvil faces paiallel io ile iliead axis.@hree W|re method@hree W|re methodO Tlis meilod is moie accuiaie ilan iwo wiiemeilod as ii ensuies alignmeni of miciomeieifaces paiallel io ile iliead axis.O Heie, iliee wiies of exacily lnown diameieis aieused, one on one side 8 ile iwo on ile oilei side.Tle wiies may be leld in land oi lung fiom asiand.O Fiom ile fig, M=diameiei ovei ile wiiesE= effeciive diameiei (io be found)d= diameiei of wiies, l=leigli of wiie cenieiabove ile piicl line, i=iadius of wiie, H=depil ofiliead, D=maioi diameiei of ile iliead.@hree W|re methodE MHABCDo/2PhEMDia 'd'oE@hree W|re method 2cot2 2cosec 1 d E M Or 2cot2 2cosec 1 2 22cot4 2rcosec 2 E M i.e.2r 2h E M wires, over the Distance2cot4 2cosec2) ( 2cot4 2HCD and 2cot2 2cot2cosec2 2cosec AB AD , ABD e triangl o oo o o oo oo o oo oPPr E rPP dCD AD h FurtherP PDE Hdthe From

)`||+ + =

)`||+ + = +)`|| + =+ + =

= == = = == =@hree W|re methodout. Iound be can E known, is d as M, oI lue correct va the Iinding AIter above. derived Iormulae using values al theoretic with the compare then & y practicall M oI value the measure can WeP 5155 . 1 d 3 D M732 . 12cot , 22ec cos , 60 , P 6495 . 0 D E0.6495P thread oI Depth threads, Metric For thread. the oI diameter maior the is D where P 605 . 1 d 1657 . 3 D M921 . 12cot and , 1657 . 22cosec 0.64P, - D E0.64P thread oI depth , 55 thread, Whitworth Foroo + = =o=o= o = = + ==o=o= = = o85@ WIk 5I2Po/2ECAP/2P/4Pitch lineBEST SIZE OF WIREB85@ WIk 5I22sec2P2sec4P2 D thread. the oI pitch the is P where4PAB line, pitch on the lies AB since Also .2sec AB 2 OB 2 D i.e.) (D wire size best oI dia21 wire oI radius OB But .2sec AB2cosAB2- 90 sinABOBOBAB2- 90 sin or ,OBABA O B Sin OAB, triangle In theline. pitch at the thread the oI portion Ilank lar to perpendicu isOB Iig in shown as words, other In thread. screw the oI diameter eIIective or line pitch at the contact makes which one the is wire size best Thebbbo=o= =o- = - =- = =o=o='+

'

o= ='+

'

o='+

'

9|tch measurementTle mosi commonly used meilods foi measuiing ile piicl aiei. Piicl measuiing macline:. Tool maleis micioscope. Sciew piicl gauge@oo| makers m|croscoe@oo| makers m|croscoeampHollow baseCollimator lensBaseColumnEye pieceOptical headMirrorwork tablewith carriage@oo| makers m|croscoe@oo| makers m|croscoei. Woiliable is placed on ile base of ile base of ile insiiumeni.:. Tle opiical lead is mounied on a veiiical column ii can be moved up and down.. Woil piece is mounied on a glass plaie.. A ligli souice piovides loiizonial beam of ligli wlicl is ieflecied fiom a miiioi by o degiee upwaids iowaids ile iable.. Image of ile ouiline of conioui of ile woil piece passes iliougl ile obieciive of ile opiical lead.. Tle image is pioiecied by a sysiem of iliee piisms io a giound glass scieen.. Tle measuiemenis aie made by means of cioss lines engiaved on ile giound glass scieen.. Tle scieen can be ioiaied iliougl o.. Diffeieni iypes of giaduaied scieens and eyepieces aie used