NPT (NPTF) and BSPT are tapered and seal on their threads, while BSPP is straight and seals with a washer, O-ring or cone. NPT threads are cut at 60° and BSP at 55°, so they’re different threads, even where the sizes nearly match.
| NPT / NPTF | BSPT | BSPP | |
|---|---|---|---|
| Shape | Tapered | Tapered | Straight (parallel) |
| Thread angle | 60° | 55° | 55° |
| Seals | On the threads, with sealant | On the threads, with sealant | With a washer, O-ring or cone on the port face, not on the thread |
| Threads per inch, 1/8" to 1" | 27, 18, 18, 14, 14, 11.5 | 28, 19, 19, 14, 14, 11 | 28, 19, 19, 14, 14, 11 |
| Where you’ll see it | Machines of US origin | Europe, Japan and many former Commonwealth countries | Europe, Japan and many former Commonwealth countries |
NPT and NPTF
Parker’s hydraulic catalogs list NPTF, the dryseal form of NPT, with the same sizes and thread counts. An NPTF male mates with an NPTF, NPSF or NPSM female, but don’t confuse it with a BSPT male. NPTF hose fittings with a 30° seat are most often seen on machines built in the US.
BSPP: the seal isn’t the thread
A BSPP thread only holds the parts together. Parker’s BSPP adapters seal with an O-ring and retaining ring or an EOlastic seal against the port’s flat face (the spotface), not in a chamfer the way an ORB port does. Hose ends with BSPP threads can also have a 30° seat or a 60° cone instead, as on JIS fittings and BS 5200 (K4) fittings, and those two look alike but can’t be interchanged.
How to tell them apart
- Check the taper. Measure across the first, fourth and last full threads. If the width changes, it’s NPT or BSPT; if it stays the same, it’s BSPP.
- Count the threads. At 1/8", 1/4", 3/8" and 1" the counts differ by one or less (27 and 28, 18 and 19, 11.5 and 11), so try an inch and a British pitch gauge.
- At 1/2" and 3/4" both have 14 threads per inch, and their male threads measure less than 0.2 mm apart. A positive identification may take an optical comparator, so look for markings or check the machine’s parts list.
- Still not sure? Use the hydraulic fitting identifier, or take the part to a hydraulic hose shop.
Joining NPT and BSP
Use an adapter made with the right thread on each end and rated for the machine’s pressure. The thread angles and most thread counts differ. For a joint that has to stay leak-free, a port with an elastomeric seal, such as an ORB port, is preferred over tapered threads, which seal poorly in dynamic use, can crack a port and can put sealant into the system. For pipe threads on water lines, see BSP vs NPT.
Know your port and hose end?
Find the adapterBefore you loosen a fitting
- Turn the machine off, put the equipment in a safe, neutral position and release the pressure before you loosen anything. Turning off the pump may not release it: check valves can hold pressure in a hose, and it can take minutes or hours to bleed away.
- Never feel for a leak with your hand or any other part of your body. Oil under pressure can go through skin, and a pinhole leak can be almost invisible.
- If oil gets under your skin, get medical help at once, even if it doesn’t hurt. An injection injury can lead to amputation.
- Threads that screw together don’t prove the parts match. Some parts that don’t belong together still thread on, and then leak or come apart under pressure.
- Use only fittings whose published working pressure is at or above your machine’s maximum pressure. If a fitting has no published rating, don’t use it.
- Stay clear the first time you run the machine under pressure after a repair.