The tool used for cutting square threads is shown in Figs. 158 and 159. It is of the proper

Table III* U. S. Standard Threads, Bolts, And Nuts

The Tap Drill Diameters in the Table Provide for a Slight Clearance at the Root of the Thread in Order to Facilitate Tapping and Reduce Tap Breakages. If Full Threads Are Required

Use the Diameters at the Root of the Threads for the Tap Drill Diameters Instead.

U. S. Standard Screw Thread

Pitch

=

1

No. of Th'ds. per Inch

Depth of Th'd

. =

0.6495 X Pitch

Width of Flat

Pitch

8

Table III U S Standard Threads Bolts And Nuts 195

Diameter

Number of Threads per Inch

Diameter at Root of Thread

DlAMETER of Tap Drill

Area in Square Inches

Tensile Strength At Stress of 6000 Pounds per Square Inch

Working Strength at Stress of 6000 Pounds per Square Inch

Dimensions of Nuts and Bolt Heads

of Bolt

at Root of Thread

Table III U S Standard Threads Bolts And Nuts 196

Table III U S Standard Threads Bolts And Nuts 197

Table III U S Standard Threads Bolts And Nuts 198

Table III U S Standard Threads Bolts And Nuts 199

Table III U S Standard Threads Bolts And Nuts 200

1/4

20

0.185

13/64

0.049

0.026

160

......

1/2

0.578

0.707

1/4

1/4

5/16

18

0.240

1/4

0.076

0.045

270

.......

19/32

0.686

0.840

5/16

19/64

3/8

16

0.294

5/16

0.110

0.068

410

.......

1 1/16

0.794

0.972

3/8

11/32

7/16

14

0.345

23/64

0.150

0.093

560

........

25/32

0.902

1.105

7/16

25/64

1/2

13

0.400

21/64

0.196

0.126

760

.........

7/8

1.011

1.237

1/2

7/16

9/16

12

0.454

15/32

0.248

0.162

1000

..........

31/32

1.119

1.370

9/16

31/64

5/8

11

0.507

1 7/32

0.307

0.202

1210

260

1 1/16

1.227

1.502

5/8

17/32

3/4

10

0.620

41/64

0.442

0.302

1810

680

1 1/4

1.444

1.768

3.

5/8

7/8

9

0.731

3/4

0.601

0.419

2520

1210

1 7/16

1.660

2.033

7/8

23/32

1

8

0.838

55/64

0.785

0.551

3300

1790

1 5/8

1.877

2.298

1

13/16

1 1/8

7

0.939

31/32

0.994

0.694

4160

2470

1 13/16

2.093

2.563

1 1/8

29/32

1 1/4

7

1.064

1 3/32

1.227

0.893

5350

3470

2

2.310

2.828

1 1/4

1

I 3/8

6

1.158

1 7/32

1.485

1.057

6340

4260

2 3/16

2.527

3.093

1 3/8

1 3/32

1 1/2

6

1.283

1 11/32

1.767

1.295

7770

5500

2 3/8

2.743

3.358

1 1/2

1 3/16

1 5/8

5 1/2

1.389

1 27/64

2.074

1.515

9090

6630

2 9/16

2.960

3.623

1 5/8

1 9/32

1 3/4

5

1.490

1 17/32

2.405

1.746

10470

7830

2 3/4

3.176

3.889

1 3/4

1 3/8

1 7/8

5

1.615

1 21/32

2.761

2.051

12300

9470

2 15/16

3.393

4.154

1 7/8

1 15/32

2

4 1/2

1.711

1 49/64

3.142

2.302

13800

10800

3 1/8

3.609

4.419

2

1 9/16

2 1/4

4 1/2

1.961

2 1/64

3.976

3.023

18100

14700

3 1/2

4.043

4.949

2 1/4

1 3/4

2 1/2

4

2.175

2 15/64

4.909

3.719

22300

18500

3 7/8

4.476

5.479

2 1/2

1 15/16

2 3/4

4

2.425

2 31/64

5.940

4.620

27700

23600

4 1/4

4.909

6.010

2 3/4

2 1/8

3

3 1/2

2.629

2 11/16

7.069

5.428

32500

28000

4 5/8

5.342

6.540

3

2 5/16

3 1/4

3 1/2

2.879

2 15/16

8.296

6.510

39000

34100

5

5.775

7.070

3 1/4

2 1/2

3 1/2

3 1/4

3.100

3 11/64

9.621

7.548

45300

40000

5 3/8

6.208

7.600

3 1/2

2 11/16

3 3/4

3

3.317

3 3/8

11.045

8.641

51800

45000

5 3/4

6.641

8.131

3 3/4

2 7/8

4

3

3.567

3 5/8

12.566

9.963

59700

50100

6 1/8

7.074

8.661

4

3 1/16

4 1/4

2 7/8

3.798

3 27/32

14.186

11.340

68000

58000

6 1/2

7.508

9.191

4 1/4

3 1/4

4 1/2

2 3/4

4.028

4 3/32

15.904

12.750

76500

66000

6 7/8

7.941

9.721

4 1/2

3

4 3/4

2 5/8

4.255

4 5/16

17.721

14.215

85500

74000

7 1/ 4

8.374

10.252

4 3/4

3 5/8

5

2 1/2

4.480

4 9/16

19.635

15.760

94000

82500

7 5/8

8.807

10.782

5

3 13/16

5 1/4

2 1/2

4.730

4 13/16

21.648

17.570

105500

93000

8

9.240

11.312

5 1/4

4

5 1/2

2 3/8

4.953

5 1/32

23.758

19.260

116000

103000

8 3/8

9.673

11.842

5 1/2

4 3/16

5 3/4

2 3/8

5.203

5 9/32

25.967

21.250

127000

114000

8 3/4

10.106

12.373

5 3/4

4 3/8

6

2 1/4

5.423

5 1/2

28.274

23.090

138000

124000

9 1/8

10.539

12.903

6

4 9/16

* Reprinted from Machinery, thickness at the cutting edge, but is somewhat narrow back of this point. The sides of the tool are inclined to the bodyas shown at AB, Fig. 159; the amount of this inclination varies with the pitch of the thread and the diameter of the piece on which the thread is to be cut. To find the inclination, draw an indefinite straight line AB; and at right angles to it draw CD, Fig. 160. Make the length of CD equal to the circumference of the thread to be cut, measured at the root of the thread. On AB, lay off from C a distance EC equal to the pitch; then draw ED. This line will represent the angle of the side of the thread. The angle of the side of the cutting tool must be a little greater for clearance.

Fig. 160. Diagram of Clearance Angle

Fig. 160. Diagram of Clearance Angle.

Cutting Tool for Inside Threads

For cutting inside threads, the shape of the cutting edge of the tool should be the same as for cutting an outside thread, and the tool must be made so that the cutting edge alone touches the work. This is accomplished by bending the tool as shown in Fig. 161, and giving it considerable clearance.