thread gauge ISO1502.pdf
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Transcript of thread gauge ISO1502.pdf
ISO1502
Ref. ISO 1502 ISO general-purpose metric screw threads - Gauges and gauging
Introduction : The purpose of this information is to explain possible causes of the problems which can arise when only
thread plug and ring gauges are used for manufacturing and inspecting threads - especially if the finished product (thread) is close to
the max. or min. tolerance limits. The ideal fit between a screw and a nut is probably best obtained with a combination of inspection (using a
GO solid gauge) and measurement, as the ideal fit should neither be to loose or too tight. Thread pitch diameter tolerances are often much
larger than most realise.
N.B. It is recommended that ISO 1502 be read as it contains more details and tables.
EXTERNAL THREAD d = Major diameter d2 = Pitch diameter d1 = Minor diameter
INTERNAL THREAD D = Major diameter D2 = Pitch diameter D1 = Minor diameter P = Pitch a = Thread angle 60O
Tolerance classes for metric threads
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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ISO1502
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 from nominal 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
above up to above up to GO
ring GO 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 15
315 500
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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ISO1502
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 and M36x4-6H nut
plus a set of GO/NO-GO M36x4-6g thread rings for a screw and a set of GO/NO-GO M36x4-6H thread 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 nut D2 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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ISO1502
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 gaugesM36x4-6g 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
(even if these two sets of gauges are within tolerance) as well as machine repeatability, probably give situations where the 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 pitch diameter measurement) with
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thread inspection (using GO thread plug and ring gauges) will the conditions for manufacturing a correct fit between screw and nut be met.
For example a M36x4-6H/6g fit should have a miimumn pitch diameter fit of 33,402 – 33,342 = 0,060 and a maximum pitch 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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