248 / 266
231
The company reserves the right to vary models and dimensions without notice.
These products are designed for industrial applications and are not suitable for sale to the general public.
Technical Data
10
NORTH AMERICAN FITTINGS & FLOW CONTROL VALVE CATALOG
>
Release 8.6
TECHNICAL DATA
PIPE THREAD SIZES
Nominal
NPT
Size
Outer
Diameter
Threads
per inch
Pitch of
Thread
1/16"
0.3125"
27 0.03704
1/8 "
0.405"
27 0.03704
1/4 "
0.540"
18 0.05556
3/8 "
0.675"
18 0.05556
1/2 "
0.840"
14 0.07143
3/4 "
1.050"
14 0.07143
1 "
1.315"
11½ 0.08696
1¼ "
1.660"
11½ 0.08696
1½ “
1.900"
11½ 0.08696
2 "
2.375"
11½ 0.08696
2½ "
2.875"
8 0.12500
3 "
3.500"
8 0.12500
4 v
4.500"
8 0.12500
National Pipe Thread Standard
Thread Form
The taper on NPT threads allows them to form a seal when torqued as the flanks of the threads
compress against each other, as opposed to straight thread fittings or compression fittings in which
the threads merely hold the pieces together and do not provide the seal. However a clearance
remains between the crests and roots of the threads, resulting in a leakage around this spiral. This
means that NPT fittings must be made leak free with the aid of thread seal tape or a thread sealant
compound. (The use of tape or sealant will also help to limit corrosion on the threads, which can
make future disassembly nearly impossible.)
There is also a semi-compatible variant called NPTF or Dryseal, designed to provide a more leak-
free seal without the use of Teflon tape or other sealant compound. NPTF threads are the same
basic shape but with crest and root heights adjusted for an interference fit, eliminating the spiral leak-
age path.
Sometimes NPT threads are referred to as MPT (Male Pipe Thread), MNPT, or NPT (M) for male
(external) threads and FPT (Female Pipe Thread), FNPT, or NPT (F) for female (internal) threads.
An equivalent designation is MIP (Male iron pipe) and FIP (Female iron pipe).