NPT, BSPP, BSPT and JIS Threads: What Is the Difference?

Choosing the correct process connection is essential when installing pressure gauges, thermometers, valves, transmitters and other industrial instrumentation. Connections that appear nearly identical may have different thread angles, pitches, tapers and sealing methods.

Four commonly encountered classifications are:

• NPT — National Pipe Taper

• BSPP — British Standard Pipe Parallel, often simply called BSP

• BSPT — British Standard Pipe Taper

• JIS — Japanese Industrial Standards connections

  
  

These threads should never be selected by appearance alone. Installing the wrong connection can damage the threads, produce an unreliable seal or create a potentially hazardous leak.

Quick comparison

Thread type	Thread shape	Thread angle	Primary sealing method	Common markets
NPT	Tapered	60°	Thread interference with suitable sealant	United States and Canada
BSPP/G	Parallel	55°	Gasket, bonded seal, O-ring or sealing seat	Europe and international equipment
BSPT/R	Tapered	55°	Thread interference with suitable sealant	Europe, Asia and international equipment
JIS B 0202	Parallel	55°	Washer, O-ring or specified sealing seat	Japanese equipment
JIS B 0203	Tapered	55°	Thread interference with suitable sealant	Japanese equipment

Conceptual thread comparison

Connection	Simplified profile	Where the seal is produced
NPT	Tapered thread: narrow at the tip and wider toward the body	Between the mating threads
BSPT	Tapered thread: narrow at the tip and wider toward the body	Between the mating threads
BSPP	Straight thread with a consistent outside diameter	At a washer, O-ring, bonded seal or metal seat
JIS parallel	Straight thread, sometimes combined with a 30° seat	At the specified seat or sealing element
JIS tapered	Tapered thread	Between the mating threads

This illustration is conceptual. Thread type should be verified by its diameter, pitch, profile and applicable standard before installation.

What is an NPT thread?

NPT stands for National Pipe Taper. It is one of the most common pipe-thread connections used on industrial instrumentation in North America.

NPT threads:

• Have a 60° thread angle

• Taper at approximately 1 in 16

• Become increasingly tight as the male and female threads are assembled

• Normally require an appropriate thread sealant

• Are commonly designated as ⅛ NPT, ¼ NPT, ½ NPT and similar sizes

The seal is created by interference between the tapered male and female threads, assisted by an application-compatible sealant such as PTFE tape or pipe-thread compound.

The sealant should be applied according to the instrument and sealant manufacturers’ instructions. Excessive sealant can enter the process line, while overtightening can damage the fitting or instrument socket.

NPT dimensions are standardized under ASME B1.20.1. ASME identifies NPT as an American tapered pipe-thread system.

What is a BSP thread?

The term BSP, meaning British Standard Pipe, describes a family of pipe threads rather than one specific connection. The two principal types are:

• BSPP — British Standard Pipe Parallel

• BSPT — British Standard Pipe Taper

Both generally use a 55° Whitworth thread form, but their sealing methods are different.

For this reason, a specification that says only “BSP” may be incomplete. It is better to identify the connection as BSPP or BSPT and specify the required sealing arrangement.

What is a BSPP thread?

BSPP stands for British Standard Pipe Parallel. It may also be identified by the letter G, such as G¼ or G½.

Unlike NPT and BSPT, a BSPP thread maintains approximately the same diameter throughout its threaded length. The threads primarily hold the connection together; they do not normally produce the pressure seal by thread interference.

Depending on the connection design, sealing may be provided by:

• A bonded sealing washer

• A flat gasket

• An O-ring

• A metal-to-metal sealing seat

• A projecting nipple or nose that contacts a mating seat

That last point is particularly important with instrumentation. Some BSPP pressure connections incorporate a nipple, spigot or cone at the end of the threaded connection. In these designs, the threads draw the two components together while the end feature creates the actual seal.

ISO 228-1 covers parallel pipe threads where pressure-tight joints are not made by the threads themselves. ISO standards catalogue

What is a BSPT thread?

BSPT stands for British Standard Pipe Taper. Its male thread is commonly designated by the letter R.

Related designations include:

• R — tapered external thread

• Rc — tapered internal thread

• Rp — parallel internal thread intended to mate with an R external thread

Like NPT, BSPT uses tapered-thread interference to help create the seal. However, BSPT has a 55° thread angle, compared with the 60° angle used by NPT.

BSPT threads are covered by ISO 7-1 and related national standards. Japanese tapered pipe threads under JIS B 0203 closely follow this thread form.

What is a JIS thread?

JIS stands for Japanese Industrial Standards. The term “JIS thread” by itself does not completely identify the connection because multiple thread and sealing configurations are used on Japanese equipment.

Two relevant pipe-thread standards are:

JIS B 0202 parallel pipe threads

JIS B 0202 covers parallel pipe threads. These use a thread form corresponding closely to BSPP or ISO 228 parallel threads.

The thread may provide the mechanical connection while sealing is accomplished by:

• A gasket or sealing washer

• An O-ring

• A 30° flare or internal cone

• Another specified seating surface

  
  

JIS B 0203 tapered pipe threads

JIS B 0203 covers tapered pipe threads used where the joint is intended to seal on the threads. Its thread geometry corresponds closely to BSPT and ISO 7 tapered threads.

JIS B 0203 uses the familiar R, Rc and Rp designations for tapered male, tapered female and compatible parallel female threads.

JIS and BSP may share threads but not sealing seats

A JIS parallel connection and a BSPP connection may have the same basic thread diameter, pitch and 55° thread form. That does not guarantee that the complete fittings are interchangeable.

For example, JIS hydraulic fittings may use a 30° flare or inverted sealing seat. Another BSPP connection may use:

• A 60° cone

• A bonded washer

• A flat-face seal

• An O-ring arrangement

  
  

The threads may screw together while the sealing surfaces fail to mate correctly. A technical reference from RYCO notes that certain JIS 30° connections use BSPP-form threads but are not interchangeable with BSPP conical-seat couplings because their sealing-seat arrangements differ. RYCO JIS thread guide

Therefore, both the thread and the sealing surface must be identified.

Can NPT and BSPT be connected?

NPT and BSPT fittings can sometimes appear to fit, especially in certain nominal sizes. This does not make them compatible.

The differences include:

Feature	NPT	BSPT
Thread angle	60°	55°
Thread profile	Flattened crest and root	Rounded crest and root
Pitch at many sizes	Different from BSPT	Different from NPT
Governing standard	ASME B1.20.1	ISO 7-1 and related standards

For example, ¼-inch NPT normally has 18 threads per inch, while ¼-inch BSPT normally has 19. At ½ inch, both may have 14 threads per inch, making visual identification more difficult even though the thread profiles remain different.

Swagelok cautions that ½-inch and ¾-inch NPT and BSPT connections can be especially difficult to distinguish accurately. Swagelok Thread and End Connection Identification Guide

Forcing one into the other can deform the threads without producing a dependable pressure seal.

How to identify an unknown thread

Use a systematic identification process:

1. Determine whether the thread is tapered or parallel.

2. Measure the outside diameter of the male thread with a caliper.

3. Measure the pitch using an inch or metric thread-pitch gauge.

4. Identify whether the thread profile is 55° or 60°.

5. Inspect the fitting for a cone, nipple, gasket face or O-ring groove.

6. Compare the measurements with the appropriate thread standard.

7. Confirm the manufacturer’s part number or data sheet whenever possible.

   
   

A nominal ¼-inch pipe thread does not measure exactly ¼ inch across the thread. Pipe-thread sizes originated from nominal pipe dimensions, so identification should not be based on outside diameter alone.

Why correct thread selection matters

Using the correct process connection helps:

• Prevent leakage

• Protect the instrument socket from cracking

• Avoid damaged or crossed threads

• Maintain the intended pressure integrity

• Simplify installation and future replacement

• Reduce reliance on adapters

• Ensure that the proper sealing method is used

  
  

Thread selection is particularly important in hydraulic, pneumatic, steam, chemical-processing and high-pressure applications. The connection material, process medium, operating pressure, temperature and vibration conditions must also be considered.

The bottom line

NPT, BSPP, BSPT and JIS connections may look similar, but they are not automatically interchangeable.

• NPT is a 60° tapered thread that seals through thread interference and suitable sealant.

• BSPP is a 55° parallel thread that normally seals against a gasket, O-ring or seating surface.

• BSPT is a 55° tapered thread that seals through thread interference and suitable sealant.

• JIS is a family of Japanese standards that includes both parallel and tapered pipe threads, sometimes combined with distinctive sealing seats.

When specifying a pressure gauge or other industrial instrument, identify the complete connection—not simply its nominal size. The thread standard, taper, pitch and sealing surface must all match.

Merit Instruments offers

with a variety of process connections to suit different equipment and application requirements. Although our most common connection threads are NPT, BSPT and BSPP, other thread sizes are available upon request.