To compare these two types of fittings, study figure
FITTINGS. The fittings used on either
wrought-iron or steel pipe are generally made of
malleable iron or cast iron. There are two types of iron
pipe fittings: the pressure type and the recessed type.
straight and reducing patterns and has female threads
screwed into one opening of this fitting and a l/2-inch
at all four branch points.
pipe into the other opening.
An iron pipe CROSS is made of malleable iron in
The pressure type of fitting is the standard fitting
used on water pipe. The recessed type of fitting, also
known as a cast-iron drainage or Durham fitting, is
generally required on all drainage lines. The recessed
type is most suitable for a smooth joint; it reduces the
probability of grease or foreign material remaining in
the joint and causing a stoppage in the line. Recessed
fittings are designed so horizontal lines entering them
A common type of iron pipe tee is the STRAIGHT
tee which has a portion that is straight through and a
90-degree takeoff on one side. All three openings of
the straight tee are of the same size. Another common
type is the REDUCING tee, similar to the straight tee
just described, except that one of the threaded
openings is of a different size than the others.
have a slope of l/4 inch per foot.
Types of iron pipe fittings include elbows, crosses,
tees, and unions The four types of elbows are 90-
degree, 45-degree, street, and reducing elbows. The
90-degree elbow changes the direction of an iron pipe
90 degrees, and a 45.degree elbow changes the
direction by 45 degrees.
STREET elbows change the direction of an iron
pipeline in a closed space where it is impractical to use
an elbow and nipple. Both 45- and 90-degree street
elbows are available. Street elbows have one female
and one male thread, rather than two female threads.
The REDUCING elbow is similar to the regular
90-degree elbow, except that one opening is smaller
than the other. For instance, a 3/4-inch pipe can be
There are two types of iron pipe unions. They are
the ground joint union and the flange union. The
GROUND JOINT union consists of three pieces, and
the FLANGE union is made in two parts. Both types
are used for joining two pipes together and are
designed so they can be disconnected easily.
Other types of iron pipe fittings include couplings,
nipples, pipe plugs, pipe caps, and pipe bushings. Each
fitting is discussed briefly.
Three common types of couplings are straight
coupling, reducer, and eccentric reducer (fig. 3-58).
The STRAIGHT COUPLING is for joining two
lengths of pipe in a straight run that do not require
additional fittings. A REDUCER joins two pipes of
different sizes. The ECCENTRIC REDUCER has two
female threads of different sizes with different centers
so, when joined, the two pieces of pipe are not in line
with each other. It is installed to provide optimum
drainage of the line.
A NIPPLE is a short length of pipe (12 inches or
less) with a male thread on each end. It is used as an
extension for a fitting. In plumbing work, nipples are
often used. Nipples are available in many precut sizes.
Figure 3-58 shows several common types of nipples.
Pipe PLUGS are fittings with male (outside)
threads. They are screwed into other fittings to close
openings. Pipe plugs have various types of heads, such
as square, slotted, and hexagon sockets (fig. 3-58).
A pipe CAP (fig. 3-58) is a fitting with female
(inside) threads. It is used like a plug. It screws on the
male thread of a piece of pipe.
Figure 3-57.Pressure and recessed (Durham) fittings.
A pipe BUSHING is a special fitting with a male
thread on the outside and a female thread on the inside
(fig. 3-58). Bushings reduce the size of openings of
fittings and valves to a smaller diameter.