Complete BSPP Thread Size Chart & Dimensions (British Standard Pipe Parallel)
What is BSPP Thread?
Technical Compliance: Our BSPP (British Standard Pipe Parallel) dimensions and thread forms strictly adhere to the ISO 228-1:2000 standard. These parallel threads (G-series) are designed for mechanical fastening and require a bonded seal or O-ring for pressure-tight connections.
Quick Navigation: What You Will Learn
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BSPP Parameters: Understanding the 55° thread angle and parallel design.
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BSPP Size Chart: Full dimensions from G 1/8" to G 4" (ISO 228-1).
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Industrial Applications: Where G threads are used in hydraulics and marine sectors.
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Measurement Guide: How to identify threads using calipers and pitch gauges.
1. What is the BSPP (G) Thread?
The BSPP (British Standard Pipe Parallel), also known as the G thread, is a globally recognized standard defined by ISO 228-1 (formerly BS 2779). It is widely used in hydraulic and pneumatic systems due to its reliability in high-pressure applications.
Key Technical Parameters:
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Thread Angle: A consistent 55° Whitworth thread form (unlike the 60° angle found in NPT).
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Parallel Design: The diameter remains constant along the entire length of the thread. It is not tapered, ensuring easy assembly.
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The "G" Designation: BSPP is technically identified by the letter G (e.g., G 1/2").
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Sealing Method: Because the threads are parallel, they do not provide a leak-proof seal on their own. They must be used with a Bonded Washer (Dowty seal), O-ring, or gasket to prevent fluid leakage.
Unlike tapered threads, BSPP relies on a constant diameter. Understanding the mechanics of coarse vs fine pitch is essential when selecting sealing washers for these parallel threads.
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Standard Range: Common sizes range from G 1/8" to G 4", covering most industrial piping and fitting requirements.
Engineering Reference: BSPP Thread Dimensions
2. BSPP (G) Thread Size Chart
| Thread (G) | Major Dia. (mm) | TPI / Pitch | Tap Drill (mm) | Action |
|---|---|---|---|---|
| G 1/8" | 9.728 | 28 / 0.907 | 8.80 | Inquiry |
| G 1/4" ★ | 13.157 | 19 / 1.337 | 11.80 | Inquiry |
| G 3/8" | 16.662 | 19 / 1.337 | 15.25 | Inquiry |
| G 1/2" ★ | 20.955 | 14 / 1.814 | 19.00 | Inquiry |
| G 5/8" | 22.911 | 14 / 1.814 | 21.00 | Inquiry |
| G 3/4" ★ | 26.441 | 14 / 1.814 | 24.50 | Inquiry |
| G 7/8" | 30.201 | 14 / 1.814 | 28.25 | Inquiry |
| G 1" | 33.249 | 11 / 2.309 | 30.75 | Inquiry |
| G 1-1/4" | 41.910 | 11 / 2.309 | 39.50 | Inquiry |
| G 1-1/2" | 47.803 | 11 / 2.309 | 45.25 | Inquiry |
| G 2" | 59.614 | 11 / 2.309 | 57.00 | Inquiry |
| G 2-1/2" | 75.184 | 11 / 2.309 | 72.60 | Inquiry |
| G 3" | 87.884 | 11 / 2.309 | 85.30 | Inquiry |
| G 4" | 113.030 | 11 / 2.309 | 110.40 | Inquiry |
Important: Do not attempt to mate NPT threads with BSPP ports. The 55° Whitworth angle of BSPP is incompatible with the 60° NPT angle, and the lack of taper will prevent a reliable seal.
Quick Guide: How to Identify Your Thread in 10 Seconds
Not sure which standard you're looking at? Use this simple 3-step checklist before you download our full guide:
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Check for Taper: Does the thread get narrower at the end?
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Yes: It’s likely NPT.
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No: It’s a parallel thread (Metric, UNF, or BSPP).
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Measure the Angle: (Use a thread pitch gauge)
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60° Angle: Standard for Metric, UNF, and NPT.
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55° Angle: Exclusive to BSPP (G) and BSPT.
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Check the Pitch:
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If the distance between threads is in Millimeters (e.g., 1.5mm, 2.0mm) → Metric.
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If you count Threads Per Inch (e.g., 20 TPI, 28 TPI) → UNF or NPT.
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This chart provides precise dimensions for BSPP (G) threads based on the ISO 228-1:2000 standard. Use these specifications to identify the correct size for hydraulic fittings and pipe connections.
Technical Notes for Sourcing Engineers:
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Standard Compliance: All data strictly follows ISO 228-1 (G thread) specifications.
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Sealing Essential: Because BSPP threads are parallel, they do not seal on the threads. You must use a Bonded Seal (Dowty Washer) or an O-ring at the base of the male thread to ensure a leak-proof connection.
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Identification Tip: When measuring a male thread, always measure the Major Diameter at its widest point.
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Example: For a G 1/2" thread, the TPI should be 14, and the diameter should measure approximately 20.955 mm.
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3.What is the application of the BSPP–British Standard Pipe Parallel Thread?
The versatility and pressure resistance of BSPP threads make them a global standard in high-performance fluid systems. Key applications include:
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Hydraulics & Pneumatics: The "Gold Standard" for connecting high-pressure hoses, valves, and cylinders in industrial machinery and presses.
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Industrial Plumbing: Reliable connections for commercial water supply, drainage systems, and industrial valves.
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Agriculture & Mining: Heavy-duty hydraulic connections for tractors, harvesters, and excavation drilling equipment.
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Automotive & Marine: Used in critical fluid lines, including brake systems, fuel lines, and shipboard hydraulic steering.
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Manufacturing: Essential for material handling systems and automated manufacturing equipment where leak-resistant seals are mandatory.
4.How to Identify and Measure BSPP Threads? (A Technical Guide for Sourcing)
Step 1: Measure the Major Diameter Use a Caliper to measure the O.D. of the male thread at its widest point. Note the measurement in mm (e.g., 20.955 mm).
Step 2: Determine the Pitch (TPI) Use a Thread Pitch Gauge or count the number of thread crests over a 1-inch distance. BSPP threads have a 55° angle.
Step 3: Check the Chart Compare your measurements with our BSPP Size Chart. If the diameter and TPI match, you have identified a G thread.
5. Conclusion
Conclusion: Choosing the right BSPP (G) thread is critical for maintaining system integrity and preventing costly leaks. By using our standard ISO 228-1 chart and proper identification techniques, you can ensure a perfect fit for your hydraulic or pneumatic needs.
Need a custom fitting or bulk quote? Contact Armpre Manufacturing today for expert engineering support.
BSPP (G) Thread Dimensions & Size Chart
Comprehensive technical dataset for British Standard Pipe Parallel (BSPP/G) threads, including major diameters, TPI (Threads Per Inch), and pitch specifications for industrial sourcing.
Identifier:
- ISO 228-1:2000
Keywords:
- BSPP Size Chart, G Thread Dimensions, TPI Chart, Hydraulic Fittings
Data Sets
Is G thread the same as BSPP?
Yes. "G" is the technical designation for BSPP (British Standard Pipe Parallel) threads defined under ISO 228-1:2000. If you see a thread marked "G 1/2," it refers to a 1/2" BSPP thread.
What is the thread angle of BSPP?
BSPP threads have a 55-degree Whitworth thread angle.
How to seal a BSPP male thread in a manifold port?
BSPP threads require a bonded washer (Dowty seal) or an O-ring with a retainer to achieve a leak-proof seal.
Is BSPP compatible with NPT threads?
No. BSPP is parallel with a 55° angle, while NPT is tapered with a 60° angle; they are not compatible.
What is the actual O.D. of a G 1/2" (1/2" BSPP) thread?
The major diameter of a G 1/2" BSPP thread is 20.955 mm (0.825 inches).
Ultimate Thread Comparison Cheat Sheet
Identify Metric, UNF, BSPP, and NPT threads in seconds. A must-have 1-page PDF guide for engineers and machinists.
Thread Standard Technical Resources
International standard M-series specifications, including coarse and fine pitch data.
Unified StandardUnified Fine thread dimensions for high-precision fasteners and aerospace applications.
American StandardTapered pipe thread reference for leak-free seals in fluid and gas systems.