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Issue 6 May 2016
New OEM Website Coming Soon
This quarter we will be launching a new OEM website.  This version of our website goes into greater technical detail about our OEM capabilities and includes information about the breadth of our OEM product experience and depth of our process expertise. We have worked hard to ensure that the site is easy to navigate and hope that once launched you will make good use of our library of technical blogs and customer case studies on the "OEM Insights" page.  Stay tuned. 


Michael Weller, General Manager, SIGMA OEM
NPT and ANPT in A Nutshell
By Jeremy Allen, Southwest
Regional Sales Manager
On a recent site visit to an OEM customer, it became apparent that there was some confusion around these two standards for screw threads.  We thought it could be helpful therefore to give a quick overview on NPT and ANPT.

As engineers, we tend to use jargon and initials as shortcuts to describe technical concepts and NPT or National Pipe Taper screw threads and ANPT or Aeronautical Pipe Taper screw threads are no exception.  Both threads are regulated by the ANSI or American National Standards Institute and are detailed in the ANSI B1.20.1 (NPT) and SAEAS71051 specifications.

NPT is one of the predominant standards in operation for waterworks applications, i.e., where water is being transported through multiples pipes and joints. ANPT, as its name suggests, originated in the Aeronautical industry and for this reason has been developed for the transportation of more hazardous or corrosive materials including gasoline, natural gas or other chemicals.

The primary differences between the two standards are that:
  • NPT requires pipe tape to make a true seal, whereas ANPT threads crush in on themselves to make a dry seal.
  • NPT and ANPT are identical up to 2 inches or smaller, whereas at 2.5 inches, the product screws are NOT identical.
  • ANPT is used for more highly technical specifications, for example in chemical processing or transportation. ANPT requires L1/L2 ring gauges for the male thread, as well as L1/L3 plug gauges for the female threads.  A crest check also known as a six step is also required to achieve the ANPT gauging.
  • The thread design used by NPT and ANPT is different; NPT uses 2 threads, while ANPT uses 3.
In addition to the above, the following features of both are worth noting:
  1. During product assembly, NPT and ANPT are designed to screw together; there is no interference between the root (the bottom of the thread form) and the crest (the top of the thread form) at the moment of assembly,
  2. Tapered screw NPTs are designed to be sealed together with some form of sealant,
  3. An NPTF screw can be used with both NPT and ANPT - there are no problems between the root and the crest
  4. Both NPT and ANPT require an L.1 gage. The L.1 gage relates to the screw thread specification.
For further information, contact To read other technical articles by SIGMA OEM engineers, see SIGMA OEM Insights.
SIGMA OEM will be out and about at a number of industry shows in 2016.  First up is the Atlantic Design and Manufacturing Show which runs June 14-16, in New York. Next on the agenda for the OEM team is MINExpo September 26-28, Las Vegas.  If you would like to arrange an appointment to meet with a SIGMA OEM representative during any of these shows, please email Sandesh Gowda at  
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