rought-iron
screw pipe should be studied, and every person interested should,
if possible, understand how these different pipes are made and how
the material of which they are composed is made. In some places one
pipe is better than another and a study of their make-up would
enlighten the user and allow him to use the best for his peculiar
conditions. The maker's name should always be on the pipe. The
following table shows the sizes, weights, and thicknesses of screw
pipe:

-------+-----------+-------------
Size | Thickness | No. threads
| | per inch
-------+-----------+-------------
1-1/4 | 0.140 | 11-1/2
1-1/2 | 0.145 | 11-1/2
2 | 0.154 | 11-1/2
2-1/2 | 0.204 | 8
3 | 0.217 | 8
3-1/2 | 0.226 | 8
4 | 0.237 | 8
5 | 0.259 | 8
6 | 0.280 | 8
-------+-----------+-------------

Screw pipe work came into common use with the advance of modern
steel structures. Some difficulty had been experienced in getting
the cast-iron pipe joints tight and to keep the pipe so anchored
that it would not crack. The screw pipe was found to answer all of
the requirements of modern structures and therefore has been used
extensively. The life of screw pipe is not as long as extra heavy
cast-iron pipe. This is the only serious objection to screw pipe,
which must be renewed after a term of years, while extra heavy cast
iron lasts indefinitely. Screw pipe is never used underground. When
piping is required underground, extra heavy cast-iron pipe is used.

PIPING

The pipe used in Durham work is galvanized extra heavy, or standard
wrought-iron, or steel pipe. It is almost impossible to recognize
wrought-iron from steel pipe without the aid of a chemical or a
magnifying glass. To test the pipe to distinguish its base, take a
sharp file and file through the surface of the pipe that is to be
tested. If the pipe is steel, under a magnifying glass the texture
of the filed surface will appear to be smooth and have small
irregular-shaped grains, and there will also be an appearance of
compactness. If the pipe is iron, the texture will have the
appearance of being ragged and will show streaks of slag or black.
When screw pipe is cut there is always left a large burr on the
inside of the pipe. This burr greatly reduces the bore of the pipe
and is a source of stoppage in