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NPT Pipe Threads, General Purpose (Inch) per ANSI/ASME B1.20.1

NPT General Purpose (Inch) Pipe Threads per ANSI/ASME B1.20.1

In 1973, American National Standards Committee B2, which had formerly been responsible for pipe thread standards, was absorbed by American National Standards Institute (ANSI) Standards Committee B1 and reorganized as Subcommittee 20. A complete rewrite of the now obsolete B2.1-1968 standard on Pipe Threads (except Dryseal) was undertaken. It was approved and formally designated as an American National Standard on February 4, 1983 and was reaffirmed in 2001 and 2006.

Specification Numbering
The system of numbering, to include metric conversions, is as follows:
ANSI/ASME B1.20.1, Pipe Threads, General Purpose (Inch)
ASME B1.20.2M-2006, Pipe Threads, 60°, General Purpose (Metric Translation)

These standards, ANSI/ASME B1.20.1 and ANSI/ASME B1.20.2M, have product thread dimensions and gaging in the same document. Thread inspection specifies the use of L1 taper thread gages similar to the long obsolete B2.1-1968. In addition, emphasis was given to the requirement that all basic thread design dimensions were to be met within the specified tolerances.

2013 Revision of ANSI/ASME B1.20.1
The 2013 revision of ANSI/ASME B1.20.1 has both significant and subtle substantive changes to the 1983 revision. It is more explanatory for the user than the previous revision.

Significant 2013 Changes:
(a) An acceptability section has been added, providing a referee method in cases of dispute. This acknowledges the potentially wide but acceptable variation in the prescribed gages and gaging methods.
(b) Figures have been updated with additional information and drawn to be more visually explanatory.
(c) The Turns of Engagement method has been moved to an appendix, due to its inherent gage correlation issues. This gaging method may be used when parties agree, but it is no longer an accepted method within the Standard.
(d) Calculated data have been revised following the rounding rules of B1.30M. This provides a standardized high level of precision in calculation. Some tabulated values changed, but no changes were deemed significant enough to affect the conformance status of products or gages. These changes are generally beyond the margin of error of the required measurements. NPTR, NPSM, and NPSL thread dimensions were not recalculated as some historical methodology, necessary for computation, was not available.
(e) Guidance for tap drill sizes has been updated to reflect varying manufacturing conditions and the wider range of available drill sizes. Instead of specifying drill sizes, the Standard now refers to the tabulated basic minor diameter of the internal thread as a reference in which to base drill size choice.
(f) Added are detailed explanations on the effects of coatings on threads, as well as guidance for pre-coating size compensation.
(g) The gaging point of reference is moved for external threads having chamfer diameters smaller than the minor diameter at the small end. This change was made to help ensure adequate thread engagement over a wider range of product thread chamfers. This change is correspondent to the existing treatment of chamfers for internal threads.
(h) The point of reference for checking wear on working gages is changed to basic. Previously, the point of reference was the size at the time of manufacture. This change facilitates the calibration of gages when the original size at manufacture is not known and standardizes gage sizes at maximum wear.
(i) Gaging guidance for straight pipe threads has been expanded, including allowing the NOGO to enter up to three turns, mimicking ASME B1.2.
(j) The use of indicating gages has been added as a gaging method.

ANSI/ASME B1.20.1 Scope
This Standard covers dimensions and gaging of pipe threads of the following series:

Related Standard: B1.20.7
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 which is based on the American National Standard Pipe Thread. By the use of this thread series, NPSH, it is possible to join small hose couplings in sizes 1⁄2 to 4, inclusive, to ends of standard pipe having American National Standard external pipe threads, using a gasket to seal the joint.

This data is provided for general information only. The intention is to provide accurate information; regardless; errors may exist in the supplied information. If accuracy is critical, base your final decisions on the data provided in the root document: B1.20.1 and B1.20.2M; which are copyrighted documents. To purchase copies visit an Authorized Reseller.

Original Posting: 12/17/2008
Last Revision: 2/2/2016
Error corrections in, or comments about, the above data can be sent to: office@gagecrib.com

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