Quick answer: The three thread standards most commonly found on industrial spray nozzles are NPT (National Pipe Tape, tapered, American standard), BSPT (British Standard Pipe Tapered, similar shape to NPT but different thread angle and pitch), and BSPP (British Standard Pipe Parallel, straight rather than tapered, typically sealed with a washer). NPT and BSPT look similar but are not interchangeable — forcing them together commonly causes leaks or thread damage.
The Three Common Thread Types
| Thread Type | Shape | Sealing Method | Common Region |
|---|---|---|---|
| NPT | Tapered | Thread deformation + sealant/tape | North America |
| BSPT | Tapered | Thread deformation + sealant/tape | UK, Europe, Asia (British-standard-influenced markets) |
| BSPP | Parallel (straight) | Bonded washer/O-ring at the base | UK, Europe, and increasingly global |
Why NPT and BSPT Are Not Interchangeable
NPT and BSPT are both tapered threads and can look nearly identical to the eye, but they differ in thread angle (60° for NPT vs. 55° for BSPT) and threads-per-inch at a given size. Threading an NPT nozzle into a BSPT fitting (or the reverse) may start engaging but will not seat correctly, resulting in a leak path even with generous sealant applied, and repeated forcing can damage the fitting’s threads. This is one of the most common causes of “the new nozzle doesn’t seal” complaints in the field.
How to Identify Your Existing Thread Type
- Check documentation first. Original equipment drawings, purchase orders, or the header manufacturer’s spec sheet are the most reliable source.
- Look at the sealing method. If the connection relies on a visible washer or O-ring seated against a flat face, it’s very likely BSPP (parallel). If it seals purely on thread engagement with tape or paste, it’s tapered — NPT or BSPT.
- Measure thread pitch and outer diameter. A thread gauge or caliper comparison against published NPT/BSPT tables is the most reliable way to distinguish tapered types from each other when documentation isn’t available.
- When in doubt, ask before ordering. Providing a supplier with a photo, a thread gauge reading, or the original equipment brand/model is faster and cheaper than a failed installation.
Practical Recommendations
Confirm thread type before ordering a replacement nozzle, not after it arrives — a mismatched thread is one of the most common (and most avoidable) causes of installation delays. When specifying new equipment or headers, standardizing on one thread type across a facility reduces the risk of a technician grabbing the wrong stock item during maintenance.
Common Mistakes
Assuming “it’s a standard pipe thread” without checking tapered vs. parallel, or NPT vs. BSPT, causes a large share of returned or re-ordered nozzles. Applying excessive thread sealant to try to force a mismatched thread to seal is a common workaround that often fails under pressure and can damage the fitting permanently.
FAQ
Can NPT and BSPT threads be used together?
No. They are both tapered but differ in thread angle and pitch, so they will not seat and seal correctly together even though they may appear similar at a glance.
How do I know if my nozzle thread is parallel or tapered?
Parallel (BSPP) connections seal against a flat face using a washer or O-ring; tapered connections (NPT/BSPT) seal by thread engagement, typically with sealant or tape.
What information should I give a supplier if I don’t know my thread type?
Photos of the connection, a thread gauge or caliper measurement, and the original equipment brand/model are usually enough for a supplier to confirm the correct thread type before shipping.
Related reading: our full spray nozzle FAQ, the spray nozzle materials guide, and the Clamp Nozzle vs Threaded Nozzle guide. Not sure of your specs? Contact us for a specification review.