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Ref. ISO 1502 ISO general-purpose metric screw threads

- Gauges and gauging

Int rodu ct ion :  

The purpose of this information is to explain possible causes of the problems which can arise when onthread plug and ring gauges

are used for manufacturing and inspecting threads - especially if the finished product (thread) is close the max. or min. tolerance limits.

he ideal fit between a screw and a nut is probably best obtained with a combination of inspection (usinGO solid gauge) and measurement,

as the ideal fit should neither be to loose or too tight. Thread pitch diameter tolerances are often muclarger than most realise.

N.B. It is recommended that ISO 1502 be read as it contains more details and tables.

 

EXTERNAL

THREAD

d = Major

diameterd2 = Pitch

diameter

d1 = Minor

diameter 

INTERNAL

THREAD

D = Major

diameter

D2 = Pitchdiameter

D1 = Minor

diameter

P = Pitch

a = Thread

angle 60O

Tolerance classes for metricthreads

 

If not specified then the pitch diameter

tolerancen for a

standard metric nut is 6H and for a

standard metric screw is 6g

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Max d2 

skrue

 

Min d2 

skrue

 

Max D2 

møtrik

 

Min D2 

møtrik

 

Td2  is the screw pitch

diameter tolerance 

TD2 is the nut pitch diameter

tolerance

D2 / D2  is the nominal pitch

diameter

es is the distance from

nominal d2

El  is the distance fromnominal D2

ZR  is the distance from the

middle of the tolerance limit

area

TR and the thread's max

limit

ZPL  is the distance from the

middle of the tolerance limit

TPL and the thread's min

limit

TR  is the manufacturing

tolerance for GO and NG ring

gauges

TPL  is the manufacturing

tolerance for GO and NG plug

gauges

Tolerances and values (mm)

 

Permissable wear on the pitchdiameter of

plug gauges and rings (mm)

Td2 / TD2 

(mm) TR TPL ZR ZPL

Td2 / TD2 (mm) WGO WNG

aboveup

toabove up to

GO

ringGO plug

NG

ring

NG

plug

-

50

80

50

80

125

8

10

14

6

7

9

-4

-2

2

0

2

6

-

50 

80 

50

80

125

10

12

16

8

9,5

12,5

7

9

12

6

7,5

9,5

125

200

200

315

18

23

11

14

8

12

12

16

125 

200 

200

315

21

25,5

17,5

21

15

19,5

11,5

15315

500

500

670

30

38

18

22

20

28

24

32

315 

500 500

670

33

41

27

33

25

31

19

23

pitch diameter tolerances for GO and NO-GO thread ring and plug

gauges

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Thread rings

Thread plug

gauges

New GO ring d2  – es  – ZR ±

TR/2

New NO-GO ring d2  – es  – 

Td2  - TR/2 ± TR/2

New GO plug D2 + El + ZPL 

± TPL/2

New NO-GO plug D2 + El +

TD2  + TPL ± TPL/2

Used GO ring d2  – es  – ZR 

+ WGO 

Used NO-GO ring d2  – es

 – ZR + WNG 

used GO plug D2  – El  – 

ZPL + WGO 

Used NO-GO plug D2 + El

 – ZPL + WNG

The calculation examples are pitch diameter tolerance limits for a standard M36x4-6g screw an

M36x4-6H nut 

us a set of GO/NO-GO M36x4-6g thread rings for a screw and a set of GO/NO-GO M36x4-6H thr

plug gauges for a nut. 

Nominal pitch diameter (d2 / D2) for a M36x4 thread is 36,000  – 2,598 = 33,402

M36x4-6g screw

d2 max = 33,402  – 0,060 =33,342

d2 min = 33,402  – 0,284 = 33,118

M36x4-6H nutD2 max = 33,402 + 0,300 = 33,702

D2 min = 33,402  – 0,000 = 33,402

d2 tolerance = 33,342  – 33,118 =

0,224 ( Td2 )

D2 tolerance = 33,702  – 33,402 =

0,300 ( TD2 )

Calculations for thread ring and plug gauge pitch

diameter tolerances

  Max Min

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New GO ring d2  – es  – ZR 

± TR/2

Used GO ring d2  – es  – ZR 

+ WGO 

New NO-GO ring d2  – es  – 

Td2  - TR/2 ± TR/2

Used NO-GO ring d2  – es  – 

ZR + WNG 

New GO dorn D2 + El + ZPL 

± TPL/2

Used GO dorn D2  – El  – 

ZPL + WGO 

New NO-GO dorn D2 + El +

TD2  + TPL ± TPL/2

Used NO-GO dorn D2 + El – ZPL + W

NG

33,402  – 0,060  – 0,012 ±

0,0115

33,402  – 0,060  – 0,012 ±

0,0255

33,402  – 0,060  – 0,224  – 

0,0115 ± 0,0115

33,402  – 0,060  – 0,224  – 

0,012 ± 0,0195

33,402 + 0 + 0,016 ± 0,007

33,402 + 0 + 0,016 ± 0,021

33,402 + 0 + 0,300 +

0,007 ± 0,007

33,402 + 0 + 0,300 +

0,007  – 0,015

33,3415

33,3555

33,1180

33,1255

 33,4250

33,4250

33,7160

33,7160

33,3185

33,3185

33,0950

33,0950

 33,4110

33,3970

33,7020

33,6940

 

Tolerances on threaded components and thread gauges

M36x4-6g

screw d2 

tolerances

M36x4-6g

thread ring d2 

tolerances

 

M36x4-6H

nut D2 

tolerances

M36x4-6H

thread plug D2 

tolerances

max 33,342

min 33,118

GO max 33,3555 / min

33,3185

NO-GO max 33,1255 /

min 33,0950

Max 33,702

Min 33,402

NO-GO max 33,7160 / min

33,6940

GO max 33,4250 / min

33,3970

Tolerances on a GO thread ring is 33,3555

 – 33,3185 = 0,0370

Tolerances on a NO-GO thread ring is

33,3555  – 33,3185 = 0,0305

Tolerances on a GO thread plug gauge is 33,7160

 – 33,6940 = 0,0220

Tolerances on a NO-GO thread pluggauge is

33,4250  – 33,0970 = 0,0328

Thread manufacturing close to either the max or min tolerance limit will, when two different sets of gauges for

manufacturing and inspection are used

ven if these two sets of gauges are within tolerance) as well as machine repeatability, probably give situations where

components could be rejected as defect.Many operators regard a "tight" fit between gauge and component as desirable. 

This approach gives increased wear on the gauge and the need for frequent callibration. 

By combining thread measurement (for example with FMS accessories and thread inserts for external and internal p

diameter measurement) with

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read inspection (using GO thread plug and ring gauges) will the conditions for manufacturing a correct fit between s

and nut be met.

r example a M36x4-6H/6g fit should have a miimumn pitch diameter fit of 33,402  – 33,342 = 0,060 and a maximum

diameterfit of 33,702  – 33,118 = 0,584.

The ideal fit (slack) between the screw and nut is 0,584  – 0,060 / 2 = 0,262 mm

There are several possibilities for thread measurement 

and inspection. The most advangeous 

(and inexpensive) is probably the combination of a "GO" thread plug or ring gauge for correct profile and 

pitch and measurement of the thread pitch diameter for  

correct positioning within tolerance limits.

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