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When using threaded pipe fittings, we may encounter different thread types, which are not interchangeable due to differing standards. To avoid errors in purchasing or failures in sealing during use, we believe it is necessary for you to have a clearer understanding of the types of threads.
What is Type Threads?
Thread types refer to the shape, size, angle, direction, and specific standards of threads, which determine how a thread connects, seals, and bears loads with other threaded fittings. The different characteristics of thread types make them suitable for various applications, such as piping, fasteners, and mechanical parts. Thread types are fundamental parameters for connections and sealing in mechanical and piping systems, and different types of threads are applicable to different regions, applications, and standards. Common thread types include: NPT, BSP, Metric, SAE, and JIS.
| Thread Type | Description | Characteristics | Applications |
| NPT | Tapered thread, according to U.S. standard | 60-degree thread angle, seals through taper | Piping connections for gas, liquid, and oil in the U.S. and Canada |
| BSP | British Standard Pipe thread, includes BSPT (tapered) and BSPP (parallel) | 55-degree thread angle; BSPT seals through taper, BSPP requires washers or O-rings for sealing | Piping systems in Europe, Asia, and Australia |
| Metric | Metric system threads, available in coarse (M) and fine (MF) pitches | 60-degree thread angle, typically requires washers or O-rings for sealing | Global applications in engineering, machinery, automotive, and construction |
| SAE | Society of Automotive Engineers standard threads | Internal taper thread with 45-degree angle; straight threads require O-rings for sealing | Hydraulic, automotive, and refrigeration systems in North America |
| JIS | Japanese Industrial Standard threads, similar to BSP threads | 55-degree thread angle; seals through taper or additional sealing elements | Various piping systems in Japan |
Common Type Threads
NPT (National Pipe Thread)
- Type: Tapered Thread
- Standard: Primarily used in the United States and Canada
- Sealing Method: Achieved through the taper of the threads; when the male and female threads are tightened, they wedge together to form a seal
- Thread Angle: 60 degrees
- Applications: Commonly used in piping, gas, and hydraulic systems
- Marking: Typically marked as “NPT” (e.g., 1/2 NPT)
- Note: This tapering allows for a tight, leak-proof connection without the need for additional sealing compounds or gaskets.
NPT Thread Chart
| Dash Size (Nominal Size) | Thread Pitch | Male Thread O.D.mm | Male Thread O.D.inches | Female Thread I.D.mm | Female Thread I.D.inches |
| -02(1/8) | 27 | 10.3 | 0.41 | 9.40 | 0.37 |
| -04(1/4) | 18 | 13.7 | 0.54 | 12.4 | 0.49 |
| -06(3/8) | 18 | 17.3 | 0.68 | 15.7 | 0.62 |
| -08(1/2) | 14 | 21.3 | 0.84 | 19.3 | 0.76 |
| -10(5/8) | 14 | 22.9 | 0.90 | 21.1 | 0.83 |
| -12(3/4) | 14 | 26.9 | 1.06 | 24.9 | 0.98 |
| -16(1) | 11 1/2 | 33.3 | 1.31 | 31.5 | 1.24 |
| -20(1 1/4) | 11 1/2 | 42.2 | 1.66 | 40.1 | 1.58 |
| -24(1 1/2) | 11 1/2 | 48.3 | 1.90 | 46.2 | 1.82 |
| -32(2) | 11 1/2 | 60.4 | 2.38 | 57.9 | 2.29 |
BSP (British Standard Pipe)
- Type: BSPT (Tapered Thread) and BSPP (Parallel Thread)
- BSPT: Tapered thread, similar to NPT but with a different thread angle.
- BSPP: Parallel (straight) thread.
- Standard: Used in the UK, Europe, Asia, and Australia.
- Sealing Method:
- BSPT: Seals through the taper of the threads.
- BSPP: Requires a washer or O-ring to achieve a seal.
- Thread Angle: 55 degrees.
- Applications: Used for water, gas, and other piping systems.
- Marking: Typically marked as “BSP” (e.g., 1/2 BSP).
BSP Thread Chart
| Dash Size (Nominal Size) | Thread Pitch | Male Thread O.D.mm | Male Thread O.D.inches | Female Thread I.D.mm | Female Thread I.D.inches |
| -02(1/8) | 28 | 9.7 | 0.38 | 8.9 | 0.35 |
| -04(1/4) | 19 | 13.2 | 0.52 | 11.9 | 0.47 |
| -06(3/8) | 19 | 16.5 | 0.65 | 15.2 | 0.6 |
| -08(1/2) | 14 | 20.8 | 0.82 | 19.1 | 0.75 |
| -10(5/8) | 14 | 22.4 | 0.88 | 20.3 | 0.8 |
| -12(3/4) | 14 | 26.4 | 1.04 | 24.6 | 0.97 |
| -16(1) | 11 | 33 | 1.3 | 31 | 1.22 |
| -20(11/4) | 11 | 41.9 | 1.65 | 39.6 | 1.56 |
| -24(11/2) | 11 | 47.8 | 1.88 | 45.5 | 1.79 |
| -32(2) | 11 | 59.7 | 2.35 | 57.4 | 2.26 |
Metric Threads
- Type: Coarse (M) and Fine (MF)
- Standard: Used globally, especially in countries using the metric system
- Sealing Method: The thread itself does not provide sealing; typically relies on washers or O-rings
- Thread Angle: 60 degrees
- Applications: Used in general engineering, machinery, automotive, and construction
- Marking: Marked as “M” followed by diameter and pitch (e.g., M10x1.5)
Metric Threads Chart
| SI Metric Port Size mm | Thrcad Pitch (mm) | Male Thread O.D (mm) | Male Thread O.D (inches) | Female Thread I.D (mm) | Female Thread I.D (inches) |
| M8 X1.0 | l | 8 | 0.315 | 6.9 | 0.272 |
| M10X 1.0 | 1 | 10 | 0.394 | 8.9 | 0.35 |
| M10X1.5 | 1.5 | 10 | 0.394 | 8.4 | 0.331 |
| M12X 1.0 | l | 12 | 0.472 | 10.9 | 0.429 |
| M12X1.5 | 1.5 | 12 | 0.472 | 10.4 | 0.409 |
| M14X1.5 | 1.5 | 14 | 0.551 | 12.4 | 0.488 |
| M16X 1.5 | 1.5 | 16 | 0.63 | 14.4 | 0.567 |
| M18X1.5 | 1.5 | 18 | 0.709 | 16.4 | 0.646 |
| M20X1.5 | 1.5 | 20 | 0.787 | 18.4 | 0.724 |
| M22X1.5 | 1.5 | 22 | 0.866 | 20.4 | 0.803 |
| M24X1.5 | 1.5 | 24 | 0.945 | 22.4 | 0.882 |
| M26X1.5 | 1.5 | 26 | 1.024 | 24.4 | 0.961 |
| M27X2.0 | 2 | 27 | 1.063 | 24.8 | 0.976 |
| M30X2.0 | 2 | 30 | 1.181 | 27.8 | 1.094 |
| M33X2.0 | 2 | 33 | 1.299 | 30.8 | 1.213 |
| M36X2.0 | 2 | 36 | 1.417 | 33.8 | 1.331 |
| M42X2.0 | 2 | 42 | 1.654 | 39.8 | 1.567 |
| M45X2.0 | 2 | 45 | 1.772 | 42.8 | 1.685 |
| M48X2.0 | 2 | 48 | 1.89 | 45.8 | 1.803 |
| M52X2.0 | 2 | 52 | 2.047 | 49.8 | 1.96 |
| M60X2.0 | 2 | 60 | 2.362 | 57.8 | 2.276 |
SAE（Society of Automotive Engineers)
- Type: SAE J512 (Internal Tapered Thread) and SAE J514 (Straight Thread with O-ring Fittings)
- Standard: Widely used in North America, especially for automotive and aerospace applications
- Sealing Method:
- SAE Internal Tapered Thread: Uses 45-degree tapered fittings
- SAE Straight Thread: Requires an O-ring for sealing
- Thread Angle: Typically 45 degrees (for tapered connections)
- Applications: Commonly used in hydraulic, automotive, and refrigeration systems
- Marking: Marked as “SAE” along with the corresponding standard number (e.g., SAE J512)
SAE Thread Chart
| Dash Size (Nominal Size) | Thread Pitch | Male Thread O.D.mm | Male Thread O.D.inches | Female Thread I.D.mm | Female Thread I.D.inches |
| -02(1/8) | 24 | 3.9 | 0.31 | 6.9 | 0.27 |
| -03(3/16) | 24 | 9.6 | 0.38 | 8.6 | 0.34 |
| -04(1/4) | 20 | 11.2 | 0.44 | 9.9 | 0.39 |
| -05(5/16) | 20 | 12.7 | 0.5 | 11.4 | 0.45 |
| -06(3/8) | 18 | 14.2 | 0.56 | 12.9 | 0.51 |
| -08(1/2) | 16 | 19 | 0.75 | 17 | 0.67 |
| -10(5/8) | 14 | 22.3 | 0.88 | 20.3 | 0.8 |
| -12(3/4) | 12 | 26.9 | 1.06 | 24.9 | 0.98 |
| – 14(7/8) | 12 | 30 | 1.18 | 27.7 | 1.09 |
| – 16(1) | 12 | 33.3 | 1.31 | 31 | 1.22 |
| – 20(11/4) | 12 | 41.4 | 1.63 | 39.1 | 1.54 |
| -24(11/2) | 12 | 47.7 | 1.88 | 45.5 | 1.79 |
| -32(2） | 12 | 63.5 | 2.5 | 61.2 | 2.41 |
JIS（Japanese Industrial Standard)
- Type: JIS B 0203 (Tapered Pipe Thread, similar to BSPT) and JIS B 0202 (Parallel Pipe Thread, similar to BSPP)
- Standard: Primarily used in Japan
- Sealing Method: Can use tapered threads for sealing or parallel threads with additional sealing elements
- Thread Angle: 55 degrees
- Applications: Commonly used in various piping systems in Japan
- Marking: Typically marked as “JIS” (e.g., JIS PT, similar to BSPT)
JIS Thread Chart
| Dash Size (Nominal Size) | Thread Pitch | Male Thread O.D.mm | Male Thread O.D.inches | FemaleThread I.D.mm | Female Thread I.D.inches |
| -02(1/8) | 28 | 9.4 | 0.37 | 8.1 | 0.32 |
| -04(1/4) | 19 | 13.7 | 0.53 | 12.4 | 0.49 |
| -06(3/8) | 19 | 17.2 | 0.68 | 16 | 0.62 |
| -08(1/2) | 14 | 21.5 | 0.84 | 19.8 | 0.77 |
| -10(5/8) | 14 | 23.1 | 0.91 | 20.6 | 0.81 |
| -12(3/4) | 14 | 26.9 | 1.06 | 25.4 | 1 |
| -16(1) | 11 | 34 | 1.34 | 31.8 | 1.25 |
| -20(11/4) | 11 | 42.6 | 1.68 | 40.4 | 1.59 |
| -24(11/2) | 11 | 48.5 | 1.9 | 46.2 | 1.81 |
| -32(2) | 11 | 60.4 | 2.37 | 58.2 | 2.29 |
Main Differences
- Thread Type and Angle: NPT (60°), BSP (55°), JIS (55°, similar to BSP), SAE (45° or straight thread), Metric (60°).
- Sealing Method: NPT and BSPT seal through the taper of the threads, while BSPP, SAE, and Metric threads usually require additional sealing elements.
- Regional Use: NPT is used in North America, BSP is used in the UK and Europe, JIS is used in Japan, SAE is used in North America, and Metric threads are used globally.
- Compatibility: NPT is not compatible with BSP due to different thread angles; JIS threads may match BSP dimensions but follow different standards; Metric threads do not match any imperial thread standards.
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How to Distinguish Different Types of Threads
Steps to Differentiate Different Types of Threads can help ensure proper matching and sealing when selecting and installing fittings. Here are the steps:
STEP 01: Measure Thread Diameter
- Use a caliper or thread gauge to measure the outer diameter of external threads (male threads) or the inner diameter of internal threads (female threads).
- Determine whether the thread size is in metric or imperial units.
STEP 02: Determine the Thread Pitch
- Use a thread pitch gauge to measure the distance between threads, known as the thread pitch.
- Identify whether the pitch is imperial (threads per inch, TPI) or metric (threads per millimeter).
STEP 03: Check the Thread Angle
- Use a thread angle gauge or refer to standard data to determine the thread angle (such as 60°, 55°, 45°, etc.).
- Different thread standards have different angles, so identifying the angle helps distinguish the standard type.
- Examples:
NPT: 60°
BSP: 55°
Metric: 60°
SAE (internal taper thread): 45°
STEP 04: Identify Thread Type (Tapered or Parallel)
- Observe the shape of the threads:
Tapered threads: The diameter gradually decreases.
Parallel threads: The diameter remains constant. - Tapered threads (e.g., NPT, BSPT) are used for self-sealing connections, while parallel threads (e.g., BSPP, Metric) usually require washers or O-rings for sealing.
STEP 05: Check Standard Markings
- Look for markings on the fitting or component, such as “NPT,” “BSPT,” “BSPP,” “SAE,” “JIS,” etc.
- Markings usually directly indicate the thread’s standard type.
STEP 06: Use a Standard Reference Table
- Based on the measured diameter, pitch, and thread angle, use a standard reference table to identify the thread type and standard.
- A reference table helps quickly identify the thread’s standard type.
STEP 07: Test Fit Compatibility
- Use a known standard threaded part to test the fit to confirm the compatibility and correctness of the thread.
- Ensure the identified thread type matches and seals properly.
By following the above steps to measure and identify threads, you can effectively differentiate different thread types (such as NPT, BSP, JIS, SAE, Metric, etc.) and ensure the correct selection of fittings and connectors.
Why SSM is Your Trusted Supplier of Threaded Pipe Fittings
SSM is your trusted supplier of threaded pipe fittings, offering a wide range of high-quality products that meet international standards such as ASME, ASTM, DIN, and JIS. With over 30 years of experience, SSM provides expert solutions, including customization options and various threading types like NPT, BSP, and Metric. Our global distribution network ensures quick delivery and excellent customer support, all at competitive prices. Committed to rigorous quality assurance, SSM delivers reliable, durable fittings tailored to meet your specific needs.
More information about Type Threads:
Different Types Of Threads And Their Uses
