The various kinds of pipe in common use are made to standard sizes, and as the draftsman very often comes in contact with piping we will consider it briefly. The kinds commonly used are wrought-iron or steel pipe, brass pipe made to the size of wrought-iron pipe, and cast-iron pipe. The cast-iron pipe is made of different weights and form, according to the purpose for which it is to be used. Standard wrought-iron pipe is rated by its nominal inside diameter, although the actual diameter does not in most cases quite agree with the nominal diameter. For example, a -inch pipe is a pipe, the hole in which is supposed to be ¼ inch in diameter, but if measured it will be found to be nearly J of an inch larger.

Standard Threads And Fittings

The threads on pipes and pipe fittings are also made to standard, and stock taps and dies made for the various sizes of pipe. These taps and dies are spoken of, or described, by stating the size of the pipe for which they are intended. For example, a ¼ - inch pipe tap is a tap of the proper size, shape, and number of threads per inch to cut the thread in a hole to receive a ¼ - inch pipe. Threaded holes are made tapering for pipes, the standard taper being ¾ inch per foot, that is, the diameter of the holes decreases at the rate of £ inch per foot. In representing a hole which is threaded with a pipe tap, the hole is drawn of a diameter at its larger end about equal to the outside diameter of the pipe which is to be screwed into it, and is drawn tapering. It is well to make the taper considerably greater than the actual taper, so that the person looking at the drawing may see at a glance that the hole is for a pipe.

Table V. Standard Sizes Of Wrought-Iron Pipe

Nominal Size

1/8

1/4

3/8

1/2

3/4

1

1 1/4

1 1/2

2

Actual Inside Diameter

.27

364

.494

.623

.824

1.048

1.38

1.611

2.067

Outside Diameter

.405

.54

.675

.84

1.05

1.315

1.66

1.90

2.375

Nominal Size

2 1/2

3

3 1/2

4

4 1/2

5

6

7

8

Actual Inside Diameter

2.468

3.067

3.548

4.026

4.508

5.045

6.065

7.023

7.982

Outside Diameter

2.875

3.50

4.00

4.50

5.00

5.563

6.625

7.625

8.625

Table VI. Standard Threads For Wrought-Iron Pipe

Nominal Size of Pipe

1/8

1/4

3/8

1/2

3/4

1

1 1/4

1 1/2

2

Threads per Inch

27

18

18

14

14

11 1/2

11 1/2

11 1/2

11 1/2

Nominal Size of Pipe

2 1/2

3

3 1/2

4

4 1/2

5

5 1/2

7

8

Threads per Inch

8

8

8

8

8

8

8

8

8

The thread is indicated in one of the conventional ways previously explained, but the number of threads per inch and the diameter of the hole need not be given; instead, a note is made that the hole is tapped for a certain size pipe. Fig. 29 illustrates this.

Tables V and VI which show the standards for wrought-iron pipe may be found convenient.