NPT Thread Calculator
for NPT thread dimensions
according to ANSI/ASME B1.20.1 standard.
- For left hand threads, include LH to the designation. (Example: 1/4 - 18 NPT - LH)
- For pressure-tight joints, it is
intended that taper pipe threads be made up wrench-tight with a sealant.
To prevent galling on
stainless steels and similar materials, the sealant usually contains a lubricant.
- For pressure-tight joints which may be used without sealant (Dryseal Compounds), check ANSI B1.20.3 standard.
- Thread taper angle = 1/16 taper = 1 deg. 47 min = 0.75 in./ft .
- The angle between the sides of the thread is 60 deg.
- Thread Designation: The nominal pipe size, number of threads per inch
and the thread series symbol in sequence. Ex: 3/8 - 18 NPT
- Standard does not include an
allowance for plating. If plating is desired, it may be
necessary to modify the threads since the same final
gauging requirements must be applied for plated and
American National Standard Taper Pipe Thread (NPT)
Notes: If the use of reamer selection is "yes" for taper pipe thread, then ream
the hole before tapping with a reamer having a taper of 3/4 inch per foot.
Note: The dimensions of the NPT Thread are given to four or five
decimal places. While this implies a greater degree of precision than is ordinarily
dimensions are the basis of gage dimensions and are so expressed for the purpose of eliminating
errors in computations.
Notea: Also length of thin ring gage and length from gauging notch to small end of plug gage.
Noteb: Also pitch diameter at gauging notch (hand-tight plane).
Notec: Also length of plug gage.
Noted: L5 from the end of the pipe determines the plane beyond which the thread form is imperfect
at the crest. The next two threads are perfect at the root. At this plane the cone formed by the crests
of the thread intersects the cylinder forming the external surface of the pipe. L5 = L2 − 2p.
Notee: Given as information for use in selecting tap drills. See
Drill Sizes for NPT Pipe
Notef: MIL—P—7105 gives the wrench makeup as three threads for 3 in. and
smaller. The E3 dimensions are then as follows for MIL—P—7105: Size 2 1⁄2 in., 2.69609 and size 3 in., 3.31719.
maximum allowable deviation in the commercial
product is one turn large or small from gages made to
the basic dimensions.
NPT Pipe Threads Manufacturing Tolerances