NPT Fittings

Q: What Is an NPT Fitting, and Where Is It Used in a Vehicle?

An NPT fitting uses the American National Standard taper pipe thread form covered by ASME B1.20.1. The male and female tapered threads wedge together as they are tightened. In automotive fluid systems, NPT adapters are commonly used at fuel pumps, regulators, pressure or temperature sensors, oil-system components, coolant ports and other threaded accessories. An NPT connection is different from an AN flare or compression connection, so buyers should match the nominal NPT size and male or female direction before selecting the adapter.

Q: How Do I Measure NPT Fittings and Choose the Correct NPT Adapter Size?

NPT thread size is nominal , so the measured outside diameter is larger than the size printed on the fitting. Measure the approximate outside diameter of a male thread with calipers, check the thread pitch with a pitch gauge, and compare both values with an NPT chart. Common reference measurements are: 1/8 NPT: approximately 0.405-inch male OD and 27 TPI 1/4 NPT: approximately 0.540-inch male OD and 18 TPI 3/8 NPT: approximately 0.675-inch male OD and 18 TPI 1/2 NPT: approximately 0.840-inch male OD and 14 TPI 3/4 NPT: approximately 1.050-inch male OD and 14 TPI 1-inch NPT: approximately 1.315-inch male OD and 11.5 TPI Because the thread is tapered, the measured diameter changes slightly along its length. Do not select a pipe thread adapter from outside diameter alone; confirm the nominal size, thread pitch and male or female direction.

Q: Are Compression Fittings NPT?

A compression fitting is not automatically an NPT fitting. “Compression” describes a sealing method in which a nut compresses a ferrule or sleeve around tubing. However, one adapter can have a compression connection on one side and a male or female NPT connection on the other. When selecting a compression fitting to NPT adapter , match the tubing outside diameter on the compression side and the nominal NPT size and gender on the threaded side. Thread tape or paste belongs only on the NPT threads when permitted, not on the compression ferrule or sealing seat.

Q: Do NPT Fittings Need Teflon Tape or Thread Sealant?

Standard NPT fittings usually require a compatible pipe thread sealant , unless the component manufacturer specifies pre-applied sealant, an NPTF dry-seal connection or another sealing method. Suitable options may include PTFE thread-seal tape , commonly called Teflon tape, or a liquid or paste sealant rated for the fitting material, fluid and operating temperature. Apply the approved sealant only to the male NPT threads and keep it back from the first thread so loose material cannot enter the system. Wrap tape in the tightening direction so it does not unwind during assembly. Do not apply NPT sealant to an AN flare seat, compression ferrule, hose barb or crush-washer sealing surface. Avoid overtightening aluminum adapters and follow the component manufacturer’s installation instructions.

Q: Can BSPT Fit into NPT?

BSPT and NPT fittings should not be connected directly. Both use tapered pipe threads, but NPT has a 60-degree thread form while BSPT uses a 55-degree thread form. Their thread pitches also differ in several common sizes. A BSPT fitting may begin to thread into an NPT port, but partial engagement does not create a correctly matched or dependable seal and can damage the threads. Use a purpose-built BSPT to NPT adapter after confirming the size and male or female direction on both components.

Connect threaded ports, hoses, gauges and fluid-system components with Evil Energy NPT fittings. This collection includes NPT adapters and pipe thread adapters for fuel, oil, cooling, air, sensor and fuel-transfer layouts. Available sizes extend from 1/8 NPT to 1 inch NPT, depending on the selected configuration.

Choose NPT Fittings by Both Connection Ends

Start with the port on your component, then identify both sides of the adapter: the nominal NPT thread size, male or female direction, and the connection required on the opposite end. Evil Energy options include NPT to NPT couplers, reducer bushings, elbows, tees, weld-on bungs, gauge-port adapters and NPT to hose barb fittings. When the other side uses a 37-degree AN flare, select a purpose-built AN to NPT adapter instead of attempting to join different thread standards directly.

Plan the Line Route Before Choosing the Adapter

Use a straight NPT fitting for a direct connection, a 45-degree or 90-degree NPT elbow to route around nearby components, a tee to add a branch, or an NPT reducer bushing to join two different nominal pipe sizes. For flexible hose connections, match the hose inside diameter as well as the NPT port size. Before installation, confirm the selected fitting’s material, supported fluid, pressure range and temperature range against the rest of the system. Review the automotive fitting selection guide when comparing NPT, AN, metric and other connection types.

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FAQs about NPT Fittings

What Is an NPT Fitting, and Where Is It Used in a Vehicle?

An NPT fitting uses the American National Standard taper pipe thread form covered by ASME B1.20.1. The male and female tapered threads wedge together as they are tightened. In automotive fluid systems, NPT adapters are commonly used at fuel pumps, regulators, pressure or temperature sensors, oil-system components, coolant ports and other threaded accessories. An NPT connection is different from an AN flare or compression connection, so buyers should match the nominal NPT size and male or female direction before selecting the adapter.

How Do I Measure NPT Fittings and Choose the Correct NPT Adapter Size?

NPT thread size is nominal, so the measured outside diameter is larger than the size printed on the fitting. Measure the approximate outside diameter of a male thread with calipers, check the thread pitch with a pitch gauge, and compare both values with an NPT chart.

Common reference measurements are:

1/8 NPT: approximately 0.405-inch male OD and 27 TPI
1/4 NPT: approximately 0.540-inch male OD and 18 TPI
3/8 NPT: approximately 0.675-inch male OD and 18 TPI
1/2 NPT: approximately 0.840-inch male OD and 14 TPI
3/4 NPT: approximately 1.050-inch male OD and 14 TPI
1-inch NPT: approximately 1.315-inch male OD and 11.5 TPI

Because the thread is tapered, the measured diameter changes slightly along its length. Do not select a pipe thread adapter from outside diameter alone; confirm the nominal size, thread pitch and male or female direction.

Are Compression Fittings NPT?

A compression fitting is not automatically an NPT fitting. “Compression” describes a sealing method in which a nut compresses a ferrule or sleeve around tubing. However, one adapter can have a compression connection on one side and a male or female NPT connection on the other. When selecting a compression fitting to NPT adapter, match the tubing outside diameter on the compression side and the nominal NPT size and gender on the threaded side. Thread tape or paste belongs only on the NPT threads when permitted, not on the compression ferrule or sealing seat.

Do NPT Fittings Need Teflon Tape or Thread Sealant?

Standard NPT fittings usually require a compatible pipe thread sealant, unless the component manufacturer specifies pre-applied sealant, an NPTF dry-seal connection or another sealing method. Suitable options may include PTFE thread-seal tape, commonly called Teflon tape, or a liquid or paste sealant rated for the fitting material, fluid and operating temperature.

Apply the approved sealant only to the male NPT threads and keep it back from the first thread so loose material cannot enter the system. Wrap tape in the tightening direction so it does not unwind during assembly. Do not apply NPT sealant to an AN flare seat, compression ferrule, hose barb or crush-washer sealing surface. Avoid overtightening aluminum adapters and follow the component manufacturer’s installation instructions.

Can BSPT Fit into NPT?

BSPT and NPT fittings should not be connected directly. Both use tapered pipe threads, but NPT has a 60-degree thread form while BSPT uses a 55-degree thread form. Their thread pitches also differ in several common sizes. A BSPT fitting may begin to thread into an NPT port, but partial engagement does not create a correctly matched or dependable seal and can damage the threads. Use a purpose-built BSPT to NPT adapter after confirming the size and male or female direction on both components.

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NPT Fittings

Choose NPT Fittings by Both Connection Ends

Plan the Line Route Before Choosing the Adapter

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