. The
description and use of these long screws will come under screw pipe
venting.

Now that the proper use of the tools has been explained, we will
proceed with the exercise according to the sketch. With a length of
pipe in the vise and the 1-inch dies in the stock, run over the
thread on the pipe. Note that all the measurements are center to
center. Screw an elbow on the pipe and measure off the first
length, which we will take as 12 inches center to center. Place the
rule on the pipe with one end of it at the center of the opening of
the elbow just screwed on. Mark 12 inches off on the pipe. This
mark represents the center of another ell. Now take another ell and
hold the center of one outlet on this mark. It will readily be seen
that to have the measurement come right, the pipe must be cut off
at a point where it will make up tight when screwed into the ell.
Therefore, about 1 inch will have to be cut off, making the pipe 1
inch shorter than where it was first marked. Cut the pipe, and
before taking it out of the vise make a thread on the pipe still in
the vise. After the thread is cut, take the reamer and ream out the
burr that is on the inside of the pipe caused by the pipe cutter.
An elbow can be screwed on this pipe. The next measurement is
marked off as explained, the pipe cut, then the piece in the vise
threaded and reamed. The measurements must be accurate and the
dies should be adjusted to cut all threads the same depth. When the
measurements are all out, there should be seven pieces of pipe,
each piece having one thread. Now the threads on the other end can
be cut except the 12 inch piece that screws into the right and left
coupling. This thread is a left-handed thread and must be cut with
the left dies. Change the dies now to the 1-inch left dies; turn
the stock in the opposite direction of the right-hand thread, and
the dies will cut the left thread. The pipe and the fittings can
easily be put together as shown in the sketch by following the
center to center measurements. The right and left coupling is the
only fitting that will cause the beginner trouble. A right and left
coupling can be used only when there is sufficient _give_ to the
pipe, that is, the two ends of the pipe to be coupled together are
only 1/2 inch apart. To get the coupling in place to start the
threads, the pipe must spread apart at least 2 inches. If the pipe
cannot be spread that much, a right and left coupling cannot be
used. The