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Pipe Threading

Pipe Threading


Threaded pipes can provide an effective seal for pipes transporting liquids,
gases, steam, and hydraulic fluid.

We thread any length of pipe in diameters ranging from 1/8” thru 20”. Tapers
available are NPT*, NPS*, 3/16” Peerless, and 8 round taper. (See fabrication
services page for larger diameters)

*National Pipe Thread is a U.S. standard for tapered (NPT) or straight (NPS)
threads used to join pipes and fittings. ANSI/ASME standard B1.20.1 covers
threads of 60-degree form with flat crests and roots in sizes from 1/16 inch to
24 inch Nominal Pipe Size. The taper rate for all NPT threads is 1/16 (3/4 inch
per foot) measured by the change of diameter (of the pipe thread) over distance.
The taper divided by a center line yields an angle 1° 47′ 24″ or 1.7899° as
measured from the center axis.


Pipe sizes do refer to physical dimensions, but the plumbing industry
standard for the sizes of pipe is not always as straight-forward as measuring
the pipe. Measuring the pipe will oftentimes mislead you into choosing the wrong
pipe, so do take care. The “pipe thread size” as shown in column 3 of the table
below is measured and based on the inside of the pipe. But, to actually
determine the size of a pipe, the outside diameter of each pipe or fitting must
be measured and compared to the table for size identification. For example, a
3/4″ NPT pipe thread has an outside diameter of 1.050 inches. Each thread size
has a defined number of threads per inch (TPI). The 3/4″ NPT pipe thread has 14
threads per inch. Both the TPI (threads per inch) and OD (outside diameter) of
the thread are required for positive identification of thread size because
several sizes have the same TPI.


All pipe thread types used in plumbing are specified by the American National
Standard for pipe as accredited by the American National Standards Institute

NPT sample (tapered threads)
National Pipe Threads (NPT)
have tapered threads. These are the most common threads used for general
purposes. NPT threads are designed with a 60 degree thread angle, and are used
for joining and sealing pipe to fittings in low pressure air or liquids and also
mechanical applications. The tapered thread is 3/4″ over one foot of length.
Tapered threads are deeper at the end of the pipe and are increasingly shallower
the further they are from the end of the pipe. The taper on the pipe only allows
the pipe to screw inside the fitting until it is forced to stop because of the
taper. The distance the pipe can be screwed into the fitting is specified by the
ANSI standard. After tightening with a wrench the threads may have slight spaces
between the pipe and fitting which could cause a leak so a pipe sealant must be
used to ensure any gaps are filled.

The Dry-seal thread (NPTF) also have tapered threads. NPTF threads are used
when the application is such that pipe sealing compounds may fail due to higher
heat or pressure than normal NPT threads can withstand. The threads are designed
to seal mechanically by slightly, but sufficiently, crushing the threads when
tightened with a wrench. This allows for joining the pipe and fitting without

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