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Pipe & Pneumatic Fittings · ASME B1.20.1 · Application guide

What Are NPT Pipe Thread Fittings Used For?

Typical applications, the industries that specify npt pipe thread fittings, and how to choose the right size, material and finish for the joint.

NPT Pipe Thread Fittings are used for joining and sealing fluid or pneumatic lines. They are manufactured to ASME B1.20.1, and selection is driven by the screw size, the fit and tolerance the assembly requires, and the service environment.

Primary duty
Joining and sealing fluid or pneumatic lines
Governing standard
ASME B1.20.1
Screw size range
1 to 312
Category
Pipe & Pneumatic Fittings

Application notes are general engineering guidance. Verify the property class and any approval requirement against your own design calculation.

What Are NPT Pipe Thread Fittings Used For? application image

The primary duty of NPT Pipe Thread Fittings is joining and sealing fluid or pneumatic lines. Below: the sectors that specify them in volume, the checklist used to select the right size and material for the application, installation notes, and the known limits of the type. Stocked across roughly 1 to 312, they cover general to heavy-duty work.

Typical Applications for NPT Pipe Thread Fittings

The most common settings where these are specified:

  • Hydraulic & fluid power: sealed, pressure-rated joints in fluid lines.
  • Process & plant piping: tapped connections on manifolds and equipment.
  • General machine building: fastening covers, brackets, motors and sub-assemblies on production equipment.
  • Maintenance & repair (MRO): a stocked size for servicing existing plant where the original fastener spec must be matched.
  • Fabrication & metalwork: bench and on-site assembly of steel frames, enclosures and weldments.

How to Specify NPT Pipe Thread Fittings for Your Application

  • Size: Match the nominal size to the mating thread or hole. This product spans 1–312; check the full table below for the exact dimensions of each size.
  • Thread & pressure: Match the thread form (BSP/NPT/metric) and pressure rating to the line, and seal appropriately (tape, sealant or O-ring).
  • Environment: For damp, coastal or chemical exposure prefer A4/316 stainless or a suitable coating; indoors, plated steel or A2 is usually sufficient.
  • Standard: This product is supplied to ASME B1.20.1. Quoting the standard on your order guarantees interchangeable dimensions between suppliers.

Installation & Assembly Practice

  • Seal tapered threads with PTFE tape or anaerobic sealant applied clear of the first thread; parallel threads seal on a washer or O-ring, not on the thread.
  • Tighten to the fitting manufacturer's torque — over-tightening tapered threads splits female ports.

Common Selection Mistakes with NPT Pipe Thread Fittings

  • Mating BSP and NPT threads directly — the 55°/60° forms do not seal against each other.
  • Exceeding the pressure rating of the lowest-rated component in the line.

Where NPT Pipe Thread Fittings Are Not the Right Choice

Do not mix thread forms (BSP into NPT) without an adapter, and do not exceed the pressure rating of the lowest-rated component.

Technical Drawing

Customize the parameters below — every spec field is editable, and the drawing redraws to match the values you choose. Changing the size will snap the other fields to that size's standard values; you can then override any individual value.

Sends the selected values to the quote form below.

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The form below follows the current technical drawing configuration. Change the drawing values above and the request details update automatically.

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Specification
Business Information

Dimensions & Specifications (ASME B1.20.1)

SizeNominal size (in)Major diameter (mm)Pitch (mm)Threads per inch (TPI)TaperReference standardNotes
1/16 NPT1/167.9380.941271:16ASME B1.20.1Tapered pipe thread, self-sealing
1/8 NPT1/810.2870.941271:16ASME B1.20.1Tapered pipe thread, self-sealing
1/4 NPT1/413.7161.411181:16ASME B1.20.1Tapered pipe thread, self-sealing
3/8 NPT3/817.1451.411181:16ASME B1.20.1Tapered pipe thread, self-sealing
1/2 NPT1/221.3361.814141:16ASME B1.20.1Tapered pipe thread, self-sealing
3/4 NPT3/426.671.814141:16ASME B1.20.1Tapered pipe thread, self-sealing
1 NPT133.4012.20911.51:16ASME B1.20.1Tapered pipe thread, self-sealing
1-1/4 NPT1-1/442.1642.20911.51:16ASME B1.20.1Tapered pipe thread, self-sealing
1-1/2 NPT1-1/248.262.20911.51:16ASME B1.20.1Tapered pipe thread, self-sealing
2 NPT260.3252.20911.51:16ASME B1.20.1Tapered pipe thread, self-sealing
2-1/2 NPT2-1/273.0253.17581:16ASME B1.20.1Tapered pipe thread, self-sealing
3 NPT388.93.17581:16ASME B1.20.1Tapered pipe thread, self-sealing
3-1/2 NPT3-1/2101.63.17581:16ASME B1.20.1Tapered pipe thread, self-sealing
4 NPT4114.33.17581:16ASME B1.20.1Tapered pipe thread, self-sealing
5 NPT5141.33.17581:16ASME B1.20.1Tapered pipe thread, self-sealing
6 NPT6168.2753.17581:16ASME B1.20.1Tapered pipe thread, self-sealing
Inside the plant

Manufactured in our own plant

This part is cold-formed, threaded, heat-treated and finished in-house. The stages below are where its class and finish are actually decided.

  1. Wire rod feeding into a cold heading machine
    01

    Cold heading

    Wire rod is drawn to size and cold-formed into blanks. Forming rather than cutting keeps the grain flow continuous around the head, which is where a bolt is most likely to fail.

    Head dimensions and under-head radius checked at set-up and per shift.

  2. Thread rolling machine producing bolt threads
    02

    Thread rolling

    Threads are rolled between hardened dies rather than cut. Rolled threads are stronger in fatigue than cut threads and hold pitch and flank angle far more consistently across a batch.

    Go / no-go ring gauges to ISO 965 tolerance class 6g.

  3. Baskets of bolts staged for heat treatment
    03

    Heat treatment

    Quench-and-temper brings carbon and alloy steel to the property class ordered — 8.8, 10.9 or 12.9 — with the furnace charge tracked so a finished lot can be traced back to it.

    Core hardness and tensile tested per lot to ISO 898-1.

  4. Zinc plated bolts in a treatment basket
    04

    Surface treatment

    Zinc, zinc-nickel, hot-dip galvanizing, black oxide, phosphate and Dacromet, selected against the service environment rather than against the price list.

    Coating thickness and neutral salt spray hours to ISO 9227.

Frequently Asked Questions

What material should NPT Pipe Thread Fittings be for outdoor use?

For damp, coastal or chemical environments specify A4 (316) stainless or a suitably coated steel. For indoor or dry use, A2 (304) stainless or zinc-plated steel is normally adequate.

Are NPT Pipe Thread Fittings made to a recognized standard?

Yes — they are manufactured to ASME B1.20.1, so dimensions are interchangeable between suppliers when you quote the standard on your order.

What are NPT Pipe Thread Fittings used for?

Joining and sealing fluid or pneumatic lines. They are supplied to ASME B1.20.1.

Which industries use NPT Pipe Thread Fittings?

They are commonly specified in hydraulic & fluid power, process & plant piping and general machine building, among other sectors.

Can I get a quote for NPT Pipe Thread Fittings in the size and material I need?

Yes. Use the technical drawing and quote form on this page to set the size and options, then send the exact configuration to our team for pricing and lead time.