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Threading

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​
DIN, DIN/ANSI​
 
 
ISO shank and square dimensions​
Shank
diameter
(DMM),mm
Square
(WSC), mm​
ISO 529
Metric​
ISO 529
UNC/UNF
BSW/BSF​
ISO2283
Metric​
ISO2284 G​ISO2284 Rc​
2.502.00​M1​
M1.2​
M1.4​
M1.6​No. 0​
M1.8​
M2​No. 1​
​2.80​2.24​M2.2​No. 2​
M2.5​No. 3​
3.15​2.50​M3​No. 4
No. 5​
M3​
3.55​2.80​M3.5​No. 6​M3.5
M4​
4.00​3.15​M4​M5​
4.50​3.55​M4.5​No. 8​M6​
5.00​4.00​M5​No. 10 3/16​
5.60​4.50​M5.5​No. 12 7/32​M7​
6.30​5.0​M6​1/4M8​
7.10​5.60​M7​9/32​
8.00​6.30​M8​5/16​M10​G1/8​Rc 1/8​
9.00​7.10​M9​M12​
10.00​8.00​M10​3/8​G1/4​Rc1/4
8.00​6.30​M11​7/16​
9.00​7.10​M12​1/2​
11.20​9.00​M14​9/16​M14​
12.50​10.00​M16​5/8​M16​G3/8​Rc3/8​
14.00​11.20​M18
M20
11/16
3/4
M18
M20​
16.00​12.50​M22​7/8​M22​
18.00​14.00​M24​1”​M24​G5/8​Rc5/8​
20.00​16.00​M27
M30
1 1/8​M27
M30​
G3/4Rc3/4​
22.40​18.00​M33​1 1/4G7/8​Rc7/8​
25.00​20.00​M36​1 3/8​G1”​Rc1”​
28.00​22.40​M39
M42​
1 1/2
 
 
DIN shank and square dimensions
Shank
diameter
(DMM), mm​
Square
(WSC), mm​
DIN
352​
DIN
371​
DIN
376​
DIN
374​
DIN
2182​
DIN
2183​
DIN 353
DIN 374​
2.5​​2.1​​M1​M1​
M1.1​​M1.1​
M1.2​M1.1​M3.5​M3.5​1/16​
M1.4​M1.1​
M1.6​M1.6​
M1.8​M1.8​
​ 2.8​ ​​2.1 ​M2​M2​
M2.2​M2.2​M4​M4​3/32​5/32​
M2.5​M2.5​
3.20​2.4​3/16​
3.50​2.70​M3​M3​M5​M5​
4.00​3.00​M3.5​M3.5​1/8​
4.50​3.40​M4​M4​M6​M5.5​5/32​1/4
6.00​4.90​M5 M6
M8​
M5 M6​M8​M8​3/16​5/16​
7.00​5.50​M10​M10​M9 M10​1/43/8​
8.00​6.20​M8​5/16​7/16​
9.00​7.00​M12​M12​M12​3/8​1/2​
10.00​8.00​M10​
11.00​9.00​M14​M14​M14​9/16​
12.00​9.00​M16​M16​M16​5/8​
14.00​11.00​M18​M18​M18​3/4​
16.00​12.00​M20​M20​M20​
18.00​14.50​M22 M24​M22 M24​M22 M24​7/8​
20.00​16.00​M27​M27​M27 M28​1”​
22.00​18.00​M30​M30​M30​1 1/8​
25.00​20.00​M33​M33​M33​1 1/4
28.00​22.00​M36​M36​M36​1 3/8​
32.00​24.00​M39
M42​
M39
M42​
M39 M42​1 1/2
1 5/8​
36.00​29.00​M45
M48​
M45
M48​
M45 M48​1 3/4
1 7/8​
40.00​32.00​M52​M52​2​G 1 3/4​
45.00​35.00​G 2”​
50.00​39.00​G 2 1/4
G 2 1/2
G 2 3/4
G 3”​
 
ANSI shank and square dimensions
Shank
diameter
(DMM), inch​
Square
(WSC), inch​
ASME B94.9
machine
screw sizes​
ASME B94.9
fract. sizes​
ASME B94.9
metric sizes​
0.141​​0.11​​No. 0​M1.6​
No. 1​M1.8​
No. 2​M2​
No. 3​M2.5​
No. 4​
No. 5​M3​
No. 6​M3.5​
0.168​0.131​No. 8​M4​
0.194​0.152​No. 10​M5​
0.220​0.165​No. 12​
0.255​0.191​1/4M6​
0.318​0.238​5/16​M7​
M8​
0.381​0.286​3/8​M10​
0.323​0.242​7/16​
0.367​0.275​1/2​M12​
0.429​0.322​9/16​M14​
0.480​0.360​5/8​M16​
0.542​0.406​11/16​M18​
0.590​0.442​3/4
0.652​0.489​13/16​M20​
0.697​0.523​7/8​M22​
0.760​0.570​15/16​M24​
0.800​0.600​1​M25​
0.896​0.672​1 1/16​M27​
1 1/8​
1.021​0.766​1 3/16​M30​
1 1/4
1.108​0.831​1 5/16​M33​
1 3/8​
1.233​0.925​1 7/16​M36​
1 1/2
1.305​0.979​1 5/8​M39​
1.430​1.072​1 3/4M42​
1.519​1.139​1 7/8​
1.644​1.233​2​M48​
 
JIS shank and square dimensions​
Shank diameter
(DMM), mm​
Square
(WSC), mm​
Size​
3​2.5​M1.4​
3​2.5​M1.7​
3​2.5​M2​
3​2.5​M2.3​
3​2.5​M2.5​
3​2.5​M2.6​
4​3.2​M3​
5​4​M4​
5.5​4.5​M5​
6​4.5​M6​
6.2​5​M8​
7​5.5​M10​
8.5​6.5​M12​
10.5​8​M14​
12.5​10​M16​
14​11​M18​
15​12​M20​
17​13​M22​
19​15​M24​
 
 

Tapping hole tolerances

Tolerance class, tap​Tolerance, internal thread (nut)Application​
ISO​ DIN​ ANSI
BS
ISO 1​4 H3 B​4 H​5 H​Fit without allowance​
ISO 2​6H​2B​4 G​5 G​6 H​Normal fit​​
ISO 36 G​1B​6 G​7 H​8 H​Fit with large allowance​
-​7 G​-​7 G​8 G​Loose 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 and nut. Lower tolerance (ISO 1) generates a fine fit without a gap on the flanks between screw 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 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.

 
DIN tolerances
Thread tolerance classes​
Tap tolerances zones​
 
 
ANSI tolerances
Thread tolerance classes​
Tap tolerances zones
 
 
 
 
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