Diameter in inches..

3/16

1/4

5/16

3/8

7/16

1/2

5/8

3/4

7/8

1

Threads per inch

21

20

18

16

14

12

11

10

9

8

Diameter in inches...

1-1/2

1-1/4

1-3/8

1-1/2

1-5/8

1-3/4

1-7/8

2

2-1/4

2-1/2

Threads per inch

7

7

6

6

5

5

4-1/2

4-1/2

4

4

Diameter in inches..

2-3/4

3

3-1/4

3-1/2

3-3/4

4

4-1/4

4-1/2

4-3/4

5

Threads per inch

3-1/2

3-1/2

3-1/4

3-1/4

3

3

2-7/8

2-7/8

2-3/4

2-3/4

Diameter in inches..

..5-1/4

5-1/2

5-3/4

6

Threads per inch

.2-5/8

2-5/8

2-1/2

2-1/2

Angle of threads = 55°. Depth of threads - pitch of screws. (One sixth of the depth is rounded off at top and bottom.) Number of threads to the inch in square threads = i number of those in angular threads.