Thread and Other End Forms

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Thread Forms

Trenton Pipe Nipple Company makes nipples with various thread and other end form configurations, including NPT, NPTF (Dryseal), NPSL, NPSM, Metric, UN and UNS.

Trenton also makes Plain end (no thread) nipples, Thread-one-end nipples and with Victaulic Groove. For example: a relatively popular item is a nipple with NPT thread one end and Victaulic Groove on the other; another one is a conversion nipple from NPT (US spec) to Metric by making one side with an NPT thread and the other with a metric thread.

NPT (National Pipe Thread - American National Standard, Taper Pipe Thread)

NPT is a tapered thread. It is the Standard thread for nipples in the United States.

It is important to remember that because this is a tapered thread, the end threads are 'imperfect threads' designed to act as a seal/tightener as a female NPT threaded part is mated. The thread are measured by length (can be varied as customer requires) and by the taper, which is measured with a ring gauge.

Please note that the standards require a gaging technique which involves tightening the gauge on the thread and then tapping it on a hard surface to seat the gauge, before tightening again. Please see ASTM B687.

NPTF (Dryseal USA - American - Standard Taper Pipe Thread)

NPTF is a tapered thread used for pressure tight joints; designed to seal presure-tight joints without the necessity to use sealing compounds. There are two types of NPTF threads: "Type 1" and "Type 2". It is necessary to specify the Type when ordering.

NPSL (American National Standard, Straight Pipe Thread for Loose-fitting Mechanical Joints with Locknuts)

This is the most common type of straight thread. It is used for All-Thread Nipples and Tank Nipples. We generally recommend adding slight NPT taper threads at the ends of NPSL straight threads to make starting the locknut easier.

NPSM (American National Standard, Straight Pipe Thread for Free-fitting Mechanical Joints)

This is finer, closer fitting straight thread form, sometimes used on All-Thread Nipples and Tank Nipples where tight fit and close thread contact is required. Must use the same, NPSM female threaded piece with it; NPSL will not fit - therefore ordinary locknuts cannot be used.

Metric Pipe Threads (BS - British Standard Pipe Threads for Pressure-tight Joints)

Obviously this is the metric equivalent of the NPT thread form. Not compatible with NPT.

Other Thread Forms

The other Thread Forms include:

  • PTF-ASE SHORT (Dryseal SAE Short Taper Pipe Thread)
  • NPSF - (Dryseal Standard Fuel Internal Straight Pipe Thread)
  • NPSI - (Dryseal Standard Intermediate Internal Straight Pipe Thread)
  • UN and UNS (Unified Screw Threads)

Other End Treatments

The other End Treatments include:

  • Normally ends are roller cut; leaves an inward fold to the inside of the pipe.
  • Saw cutting is an alternative to roller cutting of pipe, but that generally leaves burrs and sharp edges.
  • Reaming opens up the folded material after roller cutting.
  • Chamfering outs a bevel on the outside edge, eliminating sharp outside edges.
  • Ream & Chamfer operation together is commonly used as an end treatment.

Victaulic Grooving

Victaulic Grooving is also available. It is used with special Victaulic attachments.


Trenton's Fabrication Department offers various other end treatment, such as flaring, broaching, swaging, spinning end closed, etc. See Custom Fabrications.

Trenton Pipe Nipple Company does NOT provide engineering or application advice or information. The above information is provided as a general guideline or overview and is NOT intended to be a comprehensive statement of all the applicable technical information or data. There are numerous conditions, limiting factors and requirements set out in ASTM and other technical standards and publications which have not been discussed in these guidelines. Accordingly, the advice of a qualified engineer or other professional should be followed when choosing or applying a product. While the information provided is believed to be from reliable sources, Trenton Pipe Nipple Company is not responsible for errors and omissions in the information / data provided - users are strongly advised to consult qualified professionals.