Threads and Threading - Sportpilot.info

Machinery's Handbook 27th Edition
1864 AMERICAN PIPE THREADS
Table 4. Internal Threads in Pipe Couplings, NPSC for Pressuretight Joints with
Lubricant or Sealer ANSI/ASME B1.20.1-1983 (R2001)
Nom.Pipe-
Size
Thds.per
Inch
Minora Dia. Pitch Diameter
a As the ANSI Standard Pipe Thread form is maintained, the major and minor diameters of the internal
thread vary with the pitch diameter. All dimensions are given in inches.
b Nom.
Pipe
Thds. per
Inch
Minor
b The actual pitch diameter of the straight tapped hole will be slightly smaller than the value given
when gaged with a taper plug gage as called for in ANSI/ASME B1.20.1.
a Dia. Pitch Diameterb Min. Min. Max. Min. Min. Max.
1
⁄8 27 0.340 0.3701 0.3771 11 ⁄ 2 111 ⁄ 2 1.745 1.8142 1.8305
1
⁄4 18 0.442 0.4864 0.4968 2 111 ⁄ 2 2.219 2.2881 2.3044
3
⁄8 18 0.577 0.6218 0.6322 21 ⁄ 2 8 2.650 2.7504 2.7739
1
⁄2 14 0.715 0.7717 0.7851 3 8 3.277 3.3768 3.4002
3
⁄4 14 0.925 0.9822 0.9956 31 ⁄ 2 8 3.777 3.8771 3.9005
1 111 ⁄ 2 1.161 1.2305 1.2468 4 8 4.275 4.3754 4.3988
11 ⁄ 4 111 ⁄ 2 1.506 1.5752 1.5915 … … … … …
Railing Joint Taper Pipe Threads, NPTR.—Railing joints require a rigid mechanical
thread joint with external and internal taper threads. The external thread is basically the
same as the ANSI Standard Taper Pipe Thread, except that sizes 1 ⁄ 2 through 2 inches are
shortened by 3 threads and sizes 21 ⁄ 2 through 4 inches are shortened by 4 threads to permit
the use of the larger end of the pipe thread. A recess in the fitting covers the last scratch or
imperfect threads on the pipe.
Straight Pipe Threads in Pipe Couplings, NPSC.—Threads in pipe couplings made in
accordance with the ANSI/ASME B1.20.1 specifications are straight (parallel) threads of
the same thread form as the ANSI Standard Taper Pipe Thread. They are used to form pressuretight
joints when assembled with an ANSI Standard external taper pipe thread and
made up with lubricant or sealant. These joints are recommended for comparatively low
pressures only.
Straight Pipe Threads for Mechanical Joints, NPSM, NPSL, and NPSH.—While
external and internal taper pipe threads are recommended for pipe joints in practically
every service, there are mechanical joints where straight pipe threads are used to advantage.
Three types covered by ANSI/ASME B1.20.1 are:
Loose-fitting Mechanical Joints With Locknuts (External and Internal), NPSL: This
thread is designed to produce a pipe thread having the largest diameter that it is possible to
cut on standard pipe. The dimensions of these threads are given in Table 5. It will be noted
that the maximum major diameter of the external thread is slightly greater than the nominal
outside diameter of the pipe. The normal manufacturer's variation in pipe diameter provides
for this increase.
Loose-fitting Mechanical Joints for Hose Couplings (External and Internal), NPSH:
Hose coupling joints are ordinarily made with straight internal and external loose-fitting
threads. There are several standards of hose threads having various diameters and pitches.
One of these is based on the ANSI Standard pipe thread and by the use of this thread series,
it is possible to join small hose couplings in sizes 1 ⁄ 2 to 4 inches, inclusive, to ends of standard
pipe having ANSI Standard External Pipe Threads, using a gasket to seal the joints.
For the hose coupling thread dimensions see ANSI Standard Hose Coupling Screw
Threads starting on page 1872.
Free-fitting Mechanical Joints for Fixtures (External and Internal), NPSM: Standard
iron, steel, and brass pipe are often used for special applications where there are no internal
pressures. Where straight thread joints are required for mechanical assemblies, straight
pipe threads are often found more suitable or convenient. Dimensions of these threads are
given in Table 5.
Copyright 2004, Industrial Press, Inc., New York, NY