Why NPT, BSPP, and ORB Threads Are Not Interchangeable

NPT (National Pipe Taper) and BSP (British Standard Pipe) are different thread standards used in industrial piping systems.

NPT threads have a 60-degree thread angle and are typically tapered. BSP threads have a 55-degree thread angle and are available in tapered (BSPT) and parallel (BSPP) configurations.

These differences affect thread engagement, sealing methods, and compatibility. Titan Fittings recommends identifying the correct standard before installing or replacing threaded components.

NPT and BSP fittings generally should not be connected directly because their thread angles, pitches, and profiles differ.

Although some sizes may appear similar and partially engage, mixing incompatible threads can result in leaks, damaged fittings, or connection failure.

Titan Fittings recommends using an appropriately rated NPT-to-BSP adapter when transitioning between thread standards.

NPT and BSP threads can be identified by measuring thread diameter and pitch, checking whether the threads are tapered or parallel, and comparing their dimensions against recognized thread standards.

NPT threads use a 60-degree thread profile, while BSP threads use a 55-degree profile.

A thread pitch gauge, caliper, and reference chart are the most practical tools for identification. Because some thread sizes are very similar, Titan Fittings recommends verifying multiple dimensions rather than relying on appearance alone.

BSPT (British Standard Pipe Taper) threads are tapered and typically use thread engagement with an appropriate sealant to create a pressure-tight connection.

BSPP (British Standard Pipe Parallel) threads have a constant diameter and generally rely on a sealing washer, O-ring, bonded seal, or another designed sealing surface.

Titan Fittings recommends confirming both the thread type and intended sealing method when choosing BSP fittings.

Yes. NPT threads commonly use a compatible thread sealant to fill the small gaps between engaged threads.

BSPT connections may also require thread sealant, while BSPP connections typically seal through a washer, O-ring, or dedicated sealing surface rather than the threads themselves.

Titan Fittings recommends using the sealing method specified for the connection and fluid service. Thread sealant should not be applied indiscriminately to every fitting type.

Start by measuring the fitting's thread diameter with a caliper and checking the thread pitch with a gauge. Next, determine whether the thread is tapered or parallel.

Compare these measurements against NPT and BSP thread charts to identify the correct standard. A visual inspection alone is not reliable because some sizes look nearly identical.

Titan Fittings offers thread identification resources to help customers verify compatibility before ordering replacement components.

For male pipe threads, use a caliper to measure the outside thread diameter. For female pipe threads, measure the internal thread diameter at an accessible reference point.

Next, determine the threads per inch (TPI) or pitch using a thread gauge. For tapered threads, measurement location matters because the diameter changes along the thread.

Titan Fittings recommends comparing the measurements with an appropriate thread standard chart rather than assuming the measured diameter equals the nominal fitting size.

Nominal Pipe Size (NPS) is a standardized designation used to identify pipe sizes. It does not always equal the actual inside or outside diameter.

For example, a nominal 1-inch pipe has a standardized outside diameter of 1.315 inches. Its inside diameter varies with wall thickness and pipe schedule.

Titan Fittings recommends checking nominal size, actual dimensions, and pipe schedule when choosing fittings, reducers, or adapters.

To identify a replacement fitting, verify the existing fitting's connection type, thread standard, nominal size, material, and pressure rating.

Also check the system's operating temperature, fluid compatibility, and sealing requirements.

Titan Fittings recommends matching the complete fitting specification rather than relying on physical appearance or approximate thread engagement. This helps reduce leakage, installation problems, and premature component failure.

Common measurement tools include a digital or vernier caliper, thread pitch gauge, ruler, and pipe-thread identification chart.

For more demanding inspections, specialized thread gauges and calibrated measuring equipment may be necessary.

Titan Fittings recommends recording thread diameter, pitch, thread type, and nominal size before ordering replacement fittings.