What is the difference between NPT and NPTF (Dryseal) threads?

Standard NPT threads are designed to be used with a sealant (like pipe dope or Teflon tape) to create a leak-free seal. NPTF (Dryseal) threads are machined to tighter tolerances, allowing the thread crests and roots to deform and create a metal-to-metal seal without sealant, though a lubricant is still recommended for high-pressure systems.

A collection of heavy-duty forged steel NPT and NPTF pipe fittings, including elbows, nipples, and plugs, ready for industrial use.

Steel NPT & NPTF Pipe Fittings (SAE J476)

Q: Should I use Teflon tape or pipe dope for NPT fittings?

For high-pressure hydraulic systems, pipe dope (sealant) is generally preferred as it lubricates the threads during assembly and is less likely to shred and contaminate the system. Always apply sealant to the male threads only, leaving the first two threads bare.

Q: Can I connect NPT and BSPT threads?

No. This is a common and critical mistake. NPT threads have a 60° angle, while BSPT threads have a 55° angle, and their pitches are different. Attempting to connect them will damage both fittings and will not create a secure seal.

The North American standard for tapered pipe thread. Forged, machined, and plated for the reliability your hydraulic systems demand.

The Difference Between "To Spec" and a Leak-Free Seal.

National Pipe Taper (NPT) is a foundational component in North American fluid power, but its effectiveness is entirely dependent on manufacturing precision. The seal relies on the forceful wedging of tapered threads. If the angles are off, the material weak, or the threads poorly cut, it will leak. We manufacture both standard NPT (requiring sealant) and the more robust NPTF (Dryseal) fittings to the strict tolerances of ANSI B1.20.1 and SAE J476.

This means when you install a Delphi NPT fitting, the threads engage cleanly and the taper is true. For NPTF, the thread crests and roots deform as designed to create a mechanical, metal-to-metal seal. We forge these components from high-strength carbon steel and apply a durable zinc plating to withstand demanding field conditions. When your system calls for pipe thread, don't settle for "good enough." Stock the fittings that seal right the first time.

NPT / NPTF Pipe Fitting Catalog

NPTF Pipe Female Coupling

Part #: 5000

Connects two male NPT/NPTF threaded pipes or fittings of the same size. Female NPTF threads.

NPTF Pipe Male Hex Nipple

Part #: 5404

Connects two female NPT/NPTF ports. Hexagonal body for wrench tightening. Male NPTF threads.

NPT Pipe Seamless Male Nipple

Part #: 5404N

Seamless construction nipple for connecting two female NPT ports. Male NPT threads.

NPT Hexagon Pipe Male Long Nipple

Part #: 5404L

An extended length hex nipple for connecting female NPT ports with added reach. Male NPT threads.

NPTF Pipe Internal External Connector

Part #: 5405

Adapter fitting, typically male NPTF x female NPTF, for connecting different components.

NPTF Pipe Hex Reducer Bushing

Part #: 5406

Reduces port size. Male NPTF thread externally, smaller female NPTF thread internally. Hex head.

NPTF Pipe Hex Socket Plug

Part #: 5406-HP

Seals a female NPTF port. Features an internal hex (Allen) socket for flush installation.

NPTF Pipe Hex Head Plug

Part #: 5406-P

Seals a female NPTF port. Features an external hex head for easy wrench installation/removal.

NPTF Pipe Hollow Hex Head Plug

Part #: 5406-P-Hollow

Similar to a hex head plug but potentially hollow for specific applications like drainage or venting.

NPTF Pipe Square Head Plug

Part #: 5406-HP

Seals a female NPTF port. Features an external square head for specific tool engagement.

NPTF Pipe Cap

Part #: 5406C

Seals the end of a male NPT/NPTF threaded pipe or fitting. Female NPTF threads.

NPTF Pipe 90° Male Elbow

Part #: 5500

Changes flow direction by 90°. Connects two female NPTF ports. Male NPTF threads both ends.

NPTF Pipe 45° Male Elbow

Part #: 5501

Changes flow direction by 45°. Connects two female NPTF ports. Male NPTF threads both ends.

NPTF Pipe 90° Street Elbow

Part #: 5502

Changes flow direction by 90°. Connects male NPTF to female NPTF port. One male, one female NPTF end.

NPTF Pipe 45° Street Elbow

Part #: 5503

Changes flow direction by 45°. Connects male NPTF to female NPTF port. One male, one female NPTF end.

NPTF Pipe Female 90° Elbow

Part #: 5504

Changes flow direction by 90°. Connects two male NPTF pipes/fittings. Female NPTF threads both ends.

NPTF Pipe 45° Female Elbow

Part #: 5505

Changes flow direction by 45°. Connects two male NPTF pipes/fittings. Female NPTF threads both ends.

NPTF Pipe Male Tee

Part #: 5600

Creates a 90° branch from a main line. Connects three female NPTF ports. All ends male NPTF.

NPTF Female Pipe Branch Tee

Part #: 5601

Tee fitting with female NPTF threads on the branch and potentially male/female on the run ends.

NPTF Pipe Street Tee

Part #: 5602

Tee fitting typically featuring one male NPTF end and two female NPTF ends for versatile connections.

NPTF Pipe Run Tee

Part #: 5603

Tee fitting where the branch connection might differ from the main run connections.

NPTF Male Pipe Branch Tee

Part #: 5604

Tee fitting with a male NPTF thread on the 90° branch connection.

NPTF Pipe Branch Tee

Part #: 5605

A standard tee configuration for branching hydraulic lines with NPTF connections.

NPTF Pipe Female Cross

Part #: 5652

Connects four male NPTF threaded pipes or fittings at 90° angles. All ends female NPTF.

NPTF Pipe Cross

Part #: 5655

Connects four female NPTF threaded ports at 90° angles. All ends male NPTF.

NPTF Pipe Male x Pipe Swivel Male 90° Elbow

Part #: 5700

90° elbow featuring one standard male NPTF end and one male NPTF end with a swivel nut for easier installation.

37° JIC Male to NPTF Male Pipe Swivel 90° Elbow

Part #: 5701

Adapter elbow connecting a male JIC fitting to a female NPTF port at 90°, with a swivel NPTF end.

NPTF Pipe Female x Pipe Swivel Male 90° Elbow

Part #: 5702

90° elbow featuring one female NPTF end and one male NPTF end with a swivel nut for easier installation.

Using NPT & NPTF with the Rest of Your Hydraulic System

In real installations, NPT ports rarely live in isolation. They tie into hose ends, tube fittings, manifolds and imported equipment. The adapters above are designed to bridge those worlds cleanly.

NPT to JIC hose/tube lines: use adapters in our JIC 37° flare range when you want to move away from tapered threads on flexible lines and tube runs.
NPT to ORFS: where vibration or zero-clearance maintenance is a problem, convert from NPT ports to O-Ring Face Seal (ORFS) connections on hoses and manifolds.
NPT to SAE ORB: when you’re upgrading components with straight-thread O-ring ports, use SAE ORB fittings to get a more reliable, serviceable seal.
NPT vs BSPT: for imported equipment with taper threads, verify whether it’s NPT or BSPT before connecting. If it’s British taper, match it with our BSPT fittings instead of forcing an NPT part.
When corrosion is the real enemy: mirror your carbon-steel pipe thread layout in stainless NPTF fittings for marine, chemical and washdown environments.

Engineer's Guide to NPT & NPTF Pipe Fittings

While newer connection types exist, NPT remains a staple. Understanding its mechanics, limitations, and proper installation techniques is critical for preventing leaks and system failures.

Sealing Mechanism: The Interference Fit

Unlike straight threads, NPT and NPTF threads are tapered. As the male and female fittings are tightened, the threads are forced together, creating an interference fit that forms the primary seal. For standard NPT, a spiral leak path exists at the thread crests, which **must be filled with a sealant** like pipe dope or PTFE tape. For NPTF (Dryseal), the thread form is modified to ensure the crests and roots engage and deform, creating a metal-to-metal seal without the need for sealant, though a lubricant is still highly recommended.

When to Use NPT/NPTF (And When Not To)

Good For: Static, lower to medium-pressure applications where the connection will not be frequently disassembled. Common in plumbing, air systems, and some fixed hydraulic lines.
Not Good For: High-vibration systems (e.g., mobile equipment), extreme pressures, or connections that require regular servicing. In these cases, consider superior alternatives like JIC 37° Flare or O-Ring Face Seal (ORFS) fittings.

Installation Best Practices to Prevent Leaks

Inspect & Clean Threads: Ensure both male and female threads are clean and free of damage or old sealant.
Apply Sealant Correctly (Male Threads Only): If using sealant or tape, apply it only to the male threads. Leave the first 1-2 threads bare to prevent the sealant from being pushed into the hydraulic system and causing contamination.
Start by Hand: Always thread the fitting by hand for at least 2-3 turns to ensure it is not cross-threaded.
Tighten to Spec: From the hand-tight position, use a wrench to tighten the fitting an additional 2 to 3 full turns. Do not overtighten, as this can crack the female port.
Never Loosen to Align: If an elbow fitting is tightened past its desired orientation, do not back it off. Loosening a tightened NPT connection will break the seal and guarantee a leak. You must remove the fitting, re-apply sealant, and re-tighten.

For a detailed guide, see our article: How to Seal NPT Pipe Fittings: Teflon Tape vs. Pipe Dope.

Straight Answers to Common NPT Questions

What's the difference between NPT and NPTF (Dryseal)?

Standard NPT threads have a small gap at the crest and root, requiring sealant (tape or dope) to fill this leak path. NPTF (Dryseal) threads are designed to crush and deform when tightened, creating a metal-to-metal seal without sealant. However, using a lubricant is still recommended to prevent galling.

See our NPT Playbook for the full breakdown →

Should I use Teflon tape or pipe dope for NPT fittings?

Both can work. Pipe dope (sealant) is often better for high-pressure hydraulic systems as it resists vibration and helps lubricate threads. Teflon tape is clean but can shred, potentially contaminating the system. The key is to apply either sealant only to the male threads, leaving the first two threads bare.

Learn how to apply sealant like a pro →

Can I connect NPT and BSPT threads?

Absolutely not. They look similar but have different thread pitches and angles (NPT is 60°, BSPT is 55°). Attempting to connect them will damage both fittings and result in a guaranteed leak. Always verify the thread type before installation.

Read our Field Alert on NPT vs. BSPT →

Stock the Pipe Fittings That Don't Cause Headaches.

These fittings are the bread and butter of any hydraulic shop or OEM assembly line. As the direct factory, we keep a deep inventory of NPT & NPTF parts ready to ship for your wholesale needs. Get a quote for parts you can rely on.

Get a Factory-Direct Quote Need Pipe Fittings in Stainless?