JIS (Japanese Industrial Standard) Screw Thread

1 Screw ThreadTECHNICAL DATAJIS ( japanese Industrial Standard) SpecificationsCourtesy of:Note: Although these specifications are basedon JIS they also apply to ISO and DIN comments added by Maryland Metricscopyright 2002 maryland metrics/osg corporation(1) Flank : Thread face (excluding crestand root of Thread profile)(2) Crest :The tap surface joining thetwo sides or flanks of athread(3) Root :The bottom surface joiningthe flanks of two adjacentflanks(4) Angle of Thread : Angle between adjacentflanks measured at thecross section of screwthread - including the axis ofthe Screw Thread (5) Flank angle :The angle between theindividual flank and theperpendicular to the axis ofthe Thread measured in theaxial plane(6) Pitch :The distance from a pointon one Thread to acorresponding point on thenext Thread measuredparallel to the axis(7) Lead :The distance a Screw threadadvances axially in onecomplete turn(8) Lead angle.

2 Angle formed by a helixpassing a point on a flankand plane perpendicular to the axis of the Screw Thread (applies to parallelthread)(9) Major diameter of external Thread : Diameter of a virtual cylinder which touches the crest ofthe external Thread (10) Minor diameter of internal Thread : Diameter of a virtual cylinder which touches the crest ofthe internal Thread (11) Minor diameter of external Thread : Diameter of a virtual cylinder which touches the root ofthe external Thread (12) Major diameter of internal Thread : Diameter of a virtual cylinder which touches the root ofthe internal Thread (13) Pitch diameter : On a straight Screw Thread , the diameter of an imaginary cylinder wherethe width of the Thread and the width of the space threads are equal.

3 <Exterior features of Thread ridge> Screw Thread - 1 Figure 1 Basic designation of Thread (1)HalfangleofHalfangleofthreadthreadAng le of Thread (External Thread )CrestCrest clearance(Internal Thread )RootPitch PInternal threadExternal threadRoot radiusRoot clearance(Internal Thread )CrestExternal rootHeight offundamentaltriangle HMinor diameter of Internal Thread D1 Minor diameter ofexternal Thread d1 Pitch diameter d2 D1d Major diameter ofinternal Thread DMajor diameter of external threadThread overlap H1 Figure 2 Basic designation of Thread (2)Major diameter of internal threadMinor diameter of internal threadMinor diameter of external threadMajor diameter of external threadCrestThread ridgeAngle of threadInternal threadPitchFlankLeadangleThreadgroovePit ch diameterPitch diameterExternal Thread (14) Simple pitch diameter : Diameter of an imaginary cylinder when a Thread groove width,which is determined by the direction of an axis of Screw Thread ,equals half of the reference pitch.

4 For many standard taps, thesimple pitch diameter equals the pitch diameter.(15) Virtual pitch diameter : Virtual pitch diameter of a Thread with a reference pitch andreference flank angle that fit without interference and play in thethread over the given Thread engagement(16) Height of Thread :Distance between a virtual cylinder that touches a crest of thethread and a virtual cylinder that touches a root; determined bymeasuring perpendicular to the axis of the Screw Thread .(17) Height of fundamental triangle : Right angle distance between a virtual cylinder (includingthe helix) formed by extending and intersecting flanks of Thread tothe direction of crest and a virtual cylinder formed by extending andintersecting flanks of Thread to the direction of root(18) Crest truncation :The distance measured perpendicular to the axis, between thesharp crest and the cylinder or cone which bounds the actual root.

5 (19) Root truncation :The distance measured perpendicular to the axis, between thesharp root and the cylinder or cone which bounds the actual root.(20) Thread overlap :Distance measured perpendicular to the axis of the Screw threadbetween the virtual cylinder of the major diameter of external threadand the virtual cylinder of the minor diameter of internal Thread , inexternal Thread and internal Thread which mutually fit in concentric.(21) Percentage of Thread engagement : Ratio of Thread overlap in product against reference ofthread overlap(22) Length of engagement : Length measured in the direction of the Thread axis, when anexternal Thread and internal Thread are fit and mutually this length equals the length of internal Thread and includesthe chamfers of both ends of the internal Thread (23) Threaded portion :Threaded portion of tap that can be effectively used for screwthread.

6 The incomplete chamfered Thread portion is Thread - 2 Screw Thread - 3 Metric screwthreadJIS B0205 (coarse)JIS B0207 (fine)H= - - D1=d1 D2=d2P=Pitch D=For internal threadAngle of Thread is 60 . The Crest is flat, and there is clearance at the root. External Thread and internal Thread engage well. Larger root radius and lower Thread height enable easy Screw Thread processing and increase Thread Screw strength. The Major diameter of external Thread and pitch are specified by a simple numerical value (most commonly measured in millimeters).TypeEquation for Basic SizeBasic ProfileSymbolMUnified Screw threadJIS B0206 (coarse)JIS B0208 (fine)The Thread profile is same as for metric Thread .

7 Major diameter of external Thread is measured in inches and the number Thread ridges is represented by the number of Thread ridges per pipethreadJIS B0202H= - hd1=d - 2hD=d D1=d1 D2=d2 Pipe Thread mainly for mechanical coupling. It is specified according to JIS and ISO the US method, some threads have a 60 (PF)H= - - D1=d1 D2=d2P= pipethreadJIS B0203H= Thread mainly for tighter Thread portion. Taper 1/16 and 55 Thread angle. For the US method, some threads have a 60 angle R Rc(PT)Internal threadExternal 55 PrrHhH2H2h2h2 Internal threadExternal 55 PrrHhH2H2H6H6d1 or D1d2 or D2d or DHH1H2H2H4H8d1 or D1d2 or D2d or DExternal threadP60 30 30 Internal thread1690 1HH1H2H2H4H8d1 or D1d2 or D2d or DExternal threadP60 30 30 Internal Thread <Types and Applications>Note: JIS PT = BSPT JIS PF = BSPFThe following are the requirements for proper external and internal Thread engagement:1.

8 External Thread and internal Thread must have sufficient contact at the flank2. External Thread and internal Thread must have enough engagement. [SAME AS ABOVE!]In order to meet these requirements, JIS uses classes to define the limits of size and tolerancefor the major and minor diameter of internal Thread , pitch diameter, and the major and minordiameter of external ClassThe reason for setting tolerance in Thread is: 1. The ensure compatibility2. Limit the quality within a given rangeFactors that effect the quality of Screw Thread include: 1. material: type, heat processing, surface processing, uniformity, shape: root radius, incomplete Thread , roundness, surface roughness, concentration ofstress3.

9 Detentions: major diameter, pitch diameter, and minor class of Thread ridge is primarily determined by 3<Tolerance> Screw Thread - 4 External threadInternal threadSecondNameClassTypesMetric screwthread(M)GroupFirstSecondThird4h6g8 g4H, 5H5H, 6H7 HJISISOE xternal threadUnified Screw Thread (U)3A2A1A1B3B2 BJISISOJISISOW hitworth Screw Thread (W)FourthThirdUseConforming engagementClamping general machineGeneral service for general machineRegular boltInternal threadScrew Thread - 5 Angle ErrorThe difference between the actual angle of Thread and the prescribed angle of Thread . Angleslarger than the prescribed angel are " plus", while angles smaller than the prescribed angle are"minus".

10 It doubles half angle angle error: Difference between the actual flank angle and prescribed flank angleHalf angle error of Thread : Flank angle error at point where Thread profile is symmetrical tothe center line of the Thread ErrorThe difference between the actual pitch and the prescribed pitch. Pitch that is larger than theprescribed pitch is " plus", while pitch that is smaller than the prescribed pitch is "minus".Generally this is for one pitch, but some is for two error includes:Simple pitch error : Pitch error for one pitchCumulative pitch error : Total pitch error between Thread ridges which mutually depart twopitches or pitch error : Pitch error that simple pitch error is positive or negativePeriodical pitch error.