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Thread standards and tapping hole tolerances

Thread standards

Tapping tools are manufactured in five different standard: ISO, ANSI, DIN, DIN/ANSI and JIS. DIN and ISO are common world-wide, ANSI is most common in American markets and JIS is most common in Asia markets.

  • ISO, ANSI and JIS have quite short OAL (overall length) and are rather similar, except for the shank diameter which is in inch for ANSI and metric for ISO and JIS
  • DIN is a long version, with metric shank diameter and long OAL
  • DIN/ANSI is a mix of both, with ANSI shank diameter and OAL from DIN
iso_ansi_jis.jpg

ISO, ANSI, JIS

din_din_ansi.jpg

DIN, DIN/ANSI

ISO shank and square dimensions

din%20shank%20and%20square%20dimensions.jpg


Shank
diameter
(DMM),mm
Square
(WSC), mm​
ISO 529
Metric​
ISO 529
UNC/UNF
BSW/BSF​
ISO2283
Metric​
ISO2284 GISO2284 Rc
2.502.00M1
M1.2​​
M1.4​​
M1.6​
M1.8​
​M2



No. 0​

No. 1



2.802.24M2.2
M2.5
No. 2
No. 3



3.152.50M3No. 4
No. 5
M3

3.552.80M3.5No. 6M3.5
M4


4.003.15M4
M5

4.503.55M4.5No. 8M6

5.004.00M5No. 10 3/16


5.604.50M5.5No. 12 7/32M7

6.305.0M61/4M8

7.105.60M79/32


8.006.30M85/16M10G1/8Rc 1/8
9.007.10M9
M12

10.008.00M103/8
G1/4Rc1/4
8.006.30M117/16


9.007.10M121/2


11.209.00M149/16M14

12.5010.00M165/8M16G3/8Rc3/8
14.0011.20M18
M20
11/16
3/4
M18
M20


16.0012.50M227/8M22

18.0014.00M241”M24G5/8Rc5/8
20.0016.00M27
M30
1 1/8M27
M30
G3/4Rc3/4
22.4018.00M331 1/4
G7/8Rc7/8
25.0020.00M361 3/8
G1”Rc1”
28.0022.40M39
M42
1 1/2


DIN shank and square dimensions

din%20shank%20and%20square%20dimensions.jpg


Shank
diameter
(DMM), mm​
Square
(WSC), mm​
DIN 352​DIN 371​DIN 376​DIN 374​DIN 2182​DIN 2183DIN 353
DIN 374​
2.52.1M1
M1.1
M1.2
M1.4
M1.6
M1.8
M1
M1.1
M1.1
M1.1
M1.6
M1.8


M3.5




M3.5




1/16




2.82.1M2
M2.2
M2.5
M2
M2.2
M2.5

M4

M4

3/32

5/32

3.202.4




3/16
3.502.70M3M3M5M5


4.003.00M3.5M3.5

1/8

4.503.40M4M4M6M5.55/321/4
6.004.90M5 M6
M8
M5 M6M8M83/165/16
7.005.50M10
M10M9
M10
1/43/8
8.006.20
M8

5/167/16
9.007.00M12
M12M123/81/2
10.008.00
M10




11.009.00M14
M14M14
9/16
12.009.00M16
M16M16
5/8
14.0011.00M18
M18M18
3/4
16.0012.00M20
M20M20


18.0014.50M22 M24
M22 M24M22 M24
7/8
20.0016.00M27
M27M27
M28

1”
22.0018.00M30
M30M30
1 1/8
25.0020.00M33
M33M33
1 1/4
28.0022.00M36
M36M36
1 3/8
32.0024.00M39
M42

M39
M42
M39 M42
1 1/2
1 5/8

36.0029.00M45
M48

M45
M48
M45 M48
1 3/4
1 7/8

40.0032.00M52
M52

2G 1 3/4
45.0035.00





G 2”
50.0039.00





G 2 1/4
G 2 1/2
G 2 3/4
G 3”

ANSI shank and square dimensions

ansi%20shank%20and%20square%20dimensions.jpg


Shank
diameter
(DMM), inch
Square
(WSC), inch
ASME B94.9
machine
screw sizes​
ASME B94.9
fract. sizes
ASME B94.9
metric sizes​
0.1410.11No. 0
No. 1
No. 2
No. 3
No. 4
No. 5
No. 6

M1.6
M1.8
M2
M2.5

M3
M3.5
0.1680.131No. 8
M4
0.1940.152No. 10
M5
0.2200.165No. 12

0.2550.191
1/4M6
0.3180.238
5/16M7




M8
0.3810.286
3/8M10
0.3230.242
7/16
0.3670.275
1/2M12
0.4290.322
9/16M14
0.4800.360
5/8M16
0.5420.406
11/16M18
0.5900.442
3/4
0.6520.489
13/16M20
0.6970.523
7/8M22
0.7600.570
15/16M24
0.8000.600
1M25
0.8960.672
1 1/16
1 1/8
M27
1.0210.766
1 3/16
1 1/4
M30
1.1080.831
1 5/16
1 3/8
M33
1.2330.925
1 7/16
1 1/2
M36
1.3050.979
1 5/8M39
1.4301.072
1 3/4M42
1.5191.139
1 7/8
1.6441.233
2M48

JIS shank and square dimensions

jis%20shank%20and%20square%20dimensions.jpg


Shank diameter
(DMM), mm​
Square
(WSC), mm
Size
32.5M1.4
32.5M1.7
32.5M2
32.5M2.3
32.5M2.5
32.5M2.6
43.2M3
54M4
5.54.5M5
64.5M6
6.25M8
75.5M10
8.56.5M12
10.58M14
12.510M16
1411M18
1512M20
1713M22
1915M24

Tapping hole tolerances

Tolerance class, tap                                                                                         
ISODINANSIBSTolerance, internal thread (nut)Application
ISO 14 H3 B4 H     5 HFit without allowance
ISO 26H2B4 G     5 G     6 HNormal fit
ISO 36 G1B                      6 G     7 H     8 HFit with large allowance
-7 G-                                 7 G     8 GLoose fit for following
treatment or coating

Tap tolerance vs. tolerance on internal thread (nut)

Normal tap tolerance is ISO 2 (6H), which generates an average quality fit between screw thread and nut. Lower tolerance (ISO 1) generates a fine fit without a gap on the flanks between screw thread and nut. Higher tolerance (ISO 3) generates a rough fit with a large gap. This is used if the nut is coated, or if a loose fit is preferred. Between tolerances 6H (ISO2) and 6G (ISO3), and between 6G and 7G, there are also taps with tolerance 6HX and 6GX. “X” means the tolerance is outside the standard and is used for taps working with high strength or abrasive materials such as cast iron. These materials do not cause oversize problems so higher tapping hole tolerance can be used in order to increase tool life. The tolerance width is equal between 6H and 6HX. Forming taps are usually produced with a 6HX or 6GX tolerance.

Pipe threads refer to the following standards:

  • G threads to ISO 228-1. One class for internal thread (tap)
  • Rc and Rp threads to ISO 7-1
  • NPT and NPSM to ANSI B1.20.1
  • NPTF and NPSF to ANSI B1.20.3

Tolerance positioning

The tolerance width on a tap designed for a specific tolerance is much smaller than the tolerance width on the finished thread. The tap tolerance is positioned so that the tap cuts a correct thread from the start. When the tap is used, it wears gradually and will eventually be too small to cut a thread correctly, having become smaller than the lower tolerance of the GO gauge. The optimum situation would be to position the tap tolerance at the upper part of the internal thread area, but then there is a risk that the tap cuts an oversized thread, above the upper limit of the NO-GO gauge. Taps with an “X” tolerance, used for materials that do not cause oversize problems, are positioned higher. The result is a longer tool life because more wear can occur before the tap cuts a too small thread.

tolerance-positioning.jpg

DIN tolerances

din-tolerances.jpg
black-yellow.jpg
Thread tolerance classes

Tap tolerances zones

ANSI tolerances

ansi-tolerances.jpg
black-yellow.jpg
Thread tolerance classes

Tap tolerances zones

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