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Metric and inch threads and materials

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Inch Series and Metric Threads Decarburization Limits

1


Threads

Per Inch

H

Thread Height

0.75 H

From Root To Crest

Min.

0.1   H

At Root Max.

Thread

Pitch mm

H

Thread Height

mm

0.75 H

From Root To Crest

Min. mm

80

0.008

0.006

0.001

0.35

0.215

0.161

72

0.009

0.007

0.001

0.4

0.245

0.184

64

0.010

0.008

0.001

0.45

0.276

0.207

56

0.011

0.008

0.001

0.5

0.307

0.230

48

0.013

0.010

0.001

0.7

0.429

0.322

44

0.014

0.011

0.001

0.8

0.491

0.368

40

0.015

0.011

0.002

1.0

0.613

0.460

36

0.017

0.013

0.002

1.25

0.767

0.575

32

0.019

0.014

0.002

1.5

0.920

0.690

28

0.022

0.017

0.002

1.75

1.074

0.806

24

0.026

0.020

0.003

2.0

1.227

0.920

20

0.031

0.023

0.003

2.5

1.534

1.151

18

0.034

0.026

0.003

3.0

1.840

1.380

16

0.038

0.029

0.004

3.5

2.147

1.610

14

0.044

0.033

0.004

4.0

2.454

1.841

13

0.047

0.035

0.005

---

12

0.051

0.038

0.005

---

11

0.056

0.042

0.006

---

10

0.061

0.046

0.006

---

9

0.068

0.051

0.007

---

8

0.077

0.058

0.008

---

7

0.088

0.066

0.009

---

6

0.102

0.077

0.010

---

5

0.123

0.092

0.012

---

4.5

0.136

0.102

0.014

---

4

0.153

0.115

0.015

---


Thread Limiting Dimensions – Inch threads Class 3A through 1”, Class 2A 1 1/8 through 2” diameter

2


 

Coarse Series Threads


Nominal

Screw Size

Threads

Per Inch

UNRC

Pitch

Diameter Max.    Min.

Major

Diameter Max.    Min.

Minor

Diameter Min.

#2

56

0.0744

0.0728

0.0860

0.0819

0.0612

#3

48

0.0855

0.0838

0.0990

0.0945

0.0703

#4

40

0.0958

0.0939

0.1120

0.1069

0.0777

#5

40

0.1088

0.1069

0.1250

0.1199

0.0906

#6

32

0.1177

0.1156

0.1380

0.1320

0.0953

#8

32

0.1437

0.1415

0.1640

0.1580

0.1212

#10

24

0.1629

0.1604

0.1900

0.1828

0.1334

1/4

20

0.2175

0.2147

0.2500

0.2419

0.1823

5/16

18

0.2764

0.2734

0.3125

0.3038

0.2374

3/8

16

0.3344

0.3311

0.3750

0.3656

0.2906

7/16

14

0.3911

0.3876

0.4375

0.4272

0.3413

1/2

13

0.4500

0.4463

0.5000

0.4891

0.3964

5/8

11

0.5660

0.5619

0.6250

0.6129

0.5029

3/4

10

0.6850

0.6806

0.7500

0.7371

0.6157

7/8

9

0.8028

0.7981

0.8750

0.8611

0.7260

1

8

0.9188

0.9137

1.0000

0.9850

0.8325

1 1/8

7

1.0300

1.0228

1.1228

1.1064

0.9300

1 1/4

7

1.1550

1.1476

1.2478

1.2314

1.0548

1 1/2

6

1.3893

1.3812

1.4976

1.4794

1.2729

1 3/4

5

1.6174

1.6085

1.7473

1.7268

1.5092

2

4 1/2

1.8528

1.8423

1.9971

1.9751

1.6900


Thread Limiting Dimensions – Inch Series Threads

3


Fine Series Threads

Nominal

Screw Size

Threads

Per Inch

UNRF

Pitch

Diameter Max.    Min.

Major

Diameter Max.    Min.

Minor

Diameter Min.

#2

64

0.0759

0.0744

0.0860

0.0822

0.0643

#3

56

0.0874

0.0858

0.0990

0.0949

0.0742

#4

48

0.0985

0.0967

0.1120

0.1075

0.0832

#5

44

0.1102

0.1083

0.1250

0.1202

0.0936

#6

40

0.1218

0.1198

0.1380

0.1329

0.1036

#8

36

0.1460

0.1439

0.1640

0.1585

0.1259

#10

32

0.1697

0.1674

0.1900

0.1840

0.1471

1/4

28

0.2268

0.2243

0.2500

0.2435

0.2011

5/16

24

0.2854

0.2827

0.3125

0.3053

0.2557

3/8

24

0.3479

0.3450

0.3750

0.3678

0.3180

7/16

20

0.4050

0.4019

0.4375

0.4294

0.3695

1/2

20

0.4675

0.4643

0.5000

0.4919

0.4319

5/8

18

0.5889

0.5854

0.6250

0.6163

0.5494

3/4

16

0.7094

0.7056

0.7500

0.7406

0.6650

7/8

14

0.8286

0.8245

0.8750

0.8647

0.7781

1

12

0.9459

0.9415

1.0000

0.9886

0.8874

1 1/8

12

1.0691

0.0631

1.1232

1.1118

1.0090

1 1/4

12

1.1941

1.1879

1.2482

1.2368

1.1338

1 1/2

12

1.4440

1.4376

1.4981

1.4867

1.2586

1 3/4

----

2

----


Thread Limiting Dimensions – Class 4g6g Metric Threads

4


Nominal

Diameter And

Thread Pitch

Tolerance

Class

Allowance

ES

Major

Diameter Max.    Min.

Pitch

Diameter Max.    Min.

Minor

Diameter (flat form)

Max.

Minor

Diameter (rounded form)

Min. Ref.

M2x0.4

4g6g

0.019

1.981

1.886

1.721

1.679

1.548

1.433

M2.5x0.45

4g6g

0.020

2.480

2.380

2.188

2.143

1.993

1.866

M3x0.5

4g6g

0.020

2.980

2.874

2.655

2.607

2.439

2.299

M4x0.7

4g6g

0.022

3.978

3.838

3.523

3.467

3.220

3.036

M5x0.8

4g6g

0.024

4.976

4.826

4.456

4.396

4.110

3.904

M6x1.0

4g6g

0.026

5.974

5.794

5.324

5.253

4.891

4.637

M8x1.25

4g6g

0.028

7.972

7.760

7.160

7.085

6.619

6.315

M10x1.50

4g6g

0.032

9.968

9.732

8.994

8.909

8.344

7.985

M12x1.75

4g6g

0.034

11.966

11.701

10.829

10.734

10.072

9.656

M16x2.0

4g6g

0.038

15.962

15.682

14.663

14.563

13.797

13.331

M20x2.5

4g6g

0.042

19.958

19.623

18.334

18.228

17.252

16.688

M24x3.0

4g6g

0..048

23.952

23.577

22.003

21.878

20.704

20.030

M30x3.5

4g6g

0.053

29.947

29.522

27.674

27.542

26.158

25.386

M36x3.5

4g6g

0.060

35.940

35.465

33.342

33.202

31.610

30.738

  Applicable Specifications: ASME B1.13M, B1.3M


Limits for M Profile Minimum Rounded Root Radius

5

Pitch Or Thread

Spacing

Root Radius

0.125 P

Min.

0.4

0.

0.45

0.056

0.5

0.062

0.6

0.075

0.7

0.088

0.8

0.100

1.0

0.125

1.25

0.156

1.50

0.188

1.75

0.219

2.0

0.250

2.5

0.312

3.0

0.375

3.5

0.438

4.0

0.500

Applicable Specifications: ASME B1.13M, B1.3M.


Tolerance Grade and Position Symbols for Classes of ISO Metric Threads



External ThreadsInternal Threads
AmountTolerance Grade
Tolerance Grade

Major

Diameter

Pitch

Diameter

Tolerance Position (allowance)

Minor

Diameter

Pitch

Diameter

Tolerance Position (allowance)
0
-
-
h
-
-
H
Small
-
3

-
-


4
4

4
4



5

5
5


6
6
g
6
6
G

-
7

7
7


8
8

8
8


-
g

-
-

Large


e


-

ISO metric internal threads are identified by the use of capital letters for the tolerance position. ISO metric external threads are identified by the use of lower case letters for the tolerance position.

 

As an example: M6 x 1.0 – 4g6g indicates a metric thread form “M”, “6” mm nominal diameter. The fastener is externally threaded as noted by the lower case “g”. The tolerance position and grade of the major diameter is listed first – “4g”, followed by the tolerance position and grade of the pitch diameter-“6g”.


Standard Property Class 12.9 socket screw products manufactured in the United States have 4g6g thread tolerances as the form most closely resembles the 3A thread form used on inch series socket products. When plating or coating of threads is desired, a thread form with greater allowance should be selected.


Diameter and Thread Pitch Comparison

Inch

Series Size

Nom.

Dia. In.

Threads

Per Inch

Metric

Size

Dia.

In.

Pitch

In mm

Equiv.

TPI

(app.)


Inch

Series Size

Nom.

Dia. In.

Threads

Per Inch

Metric

Size

Dia.

In.

Pitch

In mm

Equiv.

TPI

(app.)




M1.4

0.05

0.3

85


1/4

0.250

20





5

0.2

127

28

#0

0.060

80






5/16

0.3125

18

24








M1.6

0.06

0.35

74





M8

0.315

1.25

20

3

0.2

127

1.0

25

#1

0.073

64






3/8

0.375

16





72

24




M2

0.07

0.4

64





M10

0.393

1.5

17

9

0.25

101

1.25

20

#2

0.086

56






7/16

0.4375

14





64

20




M2.5

0.09

0.45

56





M12

0.472

1.75

14.5

8

0.35

74

1.25

20

#3

0.099

48






1/2

0.500

13





56

20

#4

0.112

40









M14

0.551

2

12.5

48

1.5

17




M3

0.11

0.5

51


5/8

0.625

11





8

0.35

74

18

#5

0.125

40









M16

0.630

2

12.5

44

1.5

17

#6

0.138

32

40
















M4

0.15

0.7

36


3/4

0.750

10





7

0.5

51

16

#8

0.164

32









M20

0.787

2.5

10

36

1.5

17

#10

0.190

24

32
















M5

0.19

0.8

32


7/8

0.875

9





6

0.5

51

14




M6

0.23

1.0

25





M24

0.945

3

8.5

6

0.75

34

2

12.5









1

1.000

8

12






Research has shown that there are over 100 possible inch/metric fastener mismatches possible among commonly used sizes. Care must be taken not to mix the types together.


Common Tap Drill Sizes – Inch Series Threads

6

 Diameter

Pitch (TPI)

UNC

Pitch (TPI)

UNF

Drill

(in.) Decimal

Wire, Letter

Fractional

#2

56


0.070

#50



64

0.070

#50

#3

48


0.785

#53



56

0.082

#53

#4

40


0.0890

#43



48

0.0935

#42

#5

40


0.1015

#38



44

0.1040

#37

#6

32


0.1065

#36



40

0.1130

#33

#8

32


0.1360

#29



36

0.1360

#29

#10

24


0.1495

#25



32

0.1590

#21

1/4

20


0.2040

#6



28

0.2187

7/32

5/16

18


0.261

G



24

0.272

I

3/8

16


0.313

5/16



24

0.332

Q

7/16

14


0.3680

U



20

0.3906

25/64

1/2

13


0.4219

27/64



20

0.4531

29/64

5/8

11


0.5469

35/64



18

0.5781

37/64

3/4

10


0.6562

21/32



16

0.6875

11/16

7/8

9


0.7656

49/64



14

0.8125

13/16

1

8


0.875

7/8



12

0.9129

59/64

1 1/4

7


1.1094

1 7/64



12

1.1719

1 11/64

1 1/2

6


1.3437

1 11/32



12

1.4219

1 27/64


Common Tap Drill Sizes-Metric Threads

7

Metric

Diameter

Thread

Spacing In mm

Drill

mm

M2

0.4

1.

M2.5

0.45

2.05

M3

0.5

2.5

M4

0.7

3.3

M5

0.8

4.2

M6

1.0

5.0

M8

1.25

6.7

M10

1.50

8.5

M12

1.75

10.2

M16

2.0

14.0

M20

2.5

17.5

M24

3.0

21.0

M30

3.5

26.5

M36

4.0

32.0

M42

4.5

37.5

Drilling Blind Holes:  the minimum depth of a drilled hole suitable for tapping equals the full thread depth plus the number of turns, P, for each style and size of tap.
Generally, the following minimum length thread engagements are recommended: Hardened Steel – 1 times diameter of the screw
Soft Steels or Cast Iron – 1 and 1/2 times diameter of screw
Aluminum – 2 times the diameter of the screw


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