NPTF Dryseal Pipe Thread Fittings

What it is

NPTF is the American Dryseal pipe thread defined in ASME B1.20.3. Like NPT, it has a 60° thread form and a taper of 1 in 16 on the diameter. The difference is control of the crests and roots. On NPTF, the crests and roots of mating threads touch first and crush together. This gives a seal without sealant when the threads are clean and correctly made. NPT relies on sealant or tape to fill a spiral gap at the crests. Hydraulic adapters to NPTF are listed in SAE J514.

How to identify

Lay a straightedge on the male thread. Tapered threads narrow toward the end. Measure the OD and count threads per inch with a gauge. NPT and NPTF have the same OD and pitch and cannot be told apart by eye. Ask for the part marking or the original part number. NPSM is a straight thread, often used as a swivel female with a 30° internal seat.

Thread comparisons

Dash sizes for pipe threads

Key points

• NPT and NPTF will thread together, but a Dryseal seal is not assured unless both are NPTF.
• Tapered threads wedge as they tighten. Overtightening can crack cast ports and housings.
• Tapered threads are harder to reseal after repeated assembly. Many designers now use SAE ORB ports instead.
• Use sealant made for hydraulic systems, and keep it off the first threads so it does not enter the system.
• Pressure limits come from the fitting maker's data for the size and material.

Common mistakes

• Using PTFE tape that sheds into hydraulic valves.
• Matching a BSPT fitting to an NPTF port because the pitch looks close.
• Turning a tapered fitting back to orient it, which breaks the seal.

Governing standards: ASME B1.20.3 (Dryseal pipe threads, inch); SAE J514 (hydraulic tube fittings). See the fitting thread identification chart.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.