Why Thread Type Matters
Threaded connections are essential in many industries—such as plumbing, mechanical engineering, electronics, and industrial automation. Choosing the correct thread type ensures a tight fit, prevents leaks, and makes systems compatible across different regions and standards.
In this guide, we’ll explain the most common thread types you’ll encounter, how they differ, and where they are typically used. We’ll also provide a comparison table at the end for quick reference.
1. NPT – National Pipe Thread (Tapered)
Standard: ANSI/ASME B1.20.1
Thread Angle: 60°
Type: Tapered
Unit: Inch
NPT is a widely used thread in North America. It has a 1:16 taper, meaning the thread diameter decreases slightly, which helps create a tight seal.
Features:
Strong sealing due to tapered shape
Withstands high pressure and temperature
Secure and reliable connection
Easy to install
Applications:
Hydraulic systems, chemical piping, and gas delivery lines
2. PT – Pipe Thread (JIS Tapered)
Standard: JIS B 0203
Thread Angle: 55°
Type: Tapered (also known as BSPT)
Unit: Inch
PT threads are common in Asia, especially Japan, China. They also have a 1:16 taper but use a finer pitch compared to NPT.
Features:
Excellent sealing
Good pressure resistance
Requires fewer turns to install
Applications:
Pneumatics, gas fittings, water systems
3. G Thread – BSPP (British Standard Pipe Parallel)
Standard: ISO 228
Thread Angle: 55°
Type: Parallel (Cylindrical)
Unit: Inch
The G thread is part of the BSP family and is widely used in Europe and for instrumentation worldwide. Unlike PT or NPT, it is parallel, so sealing often requires an O-ring or gasket.
Features:
Highly standardized
Easy to assemble and disassemble
Strong and stable mechanical fit
Applications:
Valves, building systems, instrumentation
4. R Thread – ISO Tapered Thread (BSPT)
Standard: ISO 7-1
Thread Angle: 55°
Type: Tapered
Unit: Inch
R threads (also called BSPT) offer smooth load distribution and high precision, making them ideal for mechanical and aerospace uses.
Features:
High accuracy and tolerance
Simple structure
Good compatibility with global systems
Applications:
Precision instruments, aerospace, mechanical engineering
5. M Thread – Metric Thread
Standard: ISO 261 / ISO 724
Thread Angle: 60°
Type: Parallel
Unit: Millimeter
M threads are used globally and follow a consistent metric pitch system. A common example is M6×1 – 6 mm diameter, 1 mm pitch.
Features:
Metric-based, easy to calculate
Standardized sizes
Very versatile
Applications:
Electronics, machinery, automotive, aerospace
6. BSP – British Standard Pipe
Standards: ISO 228 (BSPP), ISO 7-1 (BSPT)
Thread Angle: 55°
Types: BSPP = Parallel, BSPT = Tapered
Unit: Inch
BSP includes two subtypes:
BSPP (G thread) – Parallel
BSPT (R or PT thread) – Tapered
Note: BSP and NPT are not compatible, even if sizes seem similar.
Applications:
Plumbing, water systems, fluid transfer
Common regions: UK, Europe, Asia, Australia
7. UN / UNF – Unified National Thread / Unified Fine Thread
Standard: ANSI/ASME B1.1
Thread Angle: 60°
Type: Parallel
Unit: Inch
These threads are used primarily for fastening, not sealing.
UN – Coarse pitch, general use
UNF – Fine pitch, stronger hold for precise parts
Applications:
Aerospace, automotive, mechanical fastening
Region: North America, aerospace industry
Comparison Table: Thread Types at a Glance
Thread Type | Standard | Angle | Taper/Parallel | Unit | Key Use | Region |
NPT | ANSI/ASME B1.20.1 | 60° | Tapered | Inch | Sealing in high-pressure systems | North America |
PT (BSPT) | JIS B 0203 | 55° | Tapered | Inch | Pneumatics, water/gas fittings | Asia (Japan, China, Taiwan) |
G (BSPP) | ISO 228 | 55° | Parallel | Inch | Valves, instrumentation | Europe, global |
R (BSPT) | ISO 7-1 | 55° | Tapered | Inch | Precision, aerospace | Worldwide |
M (Metric) | ISO 261 / ISO 724 | 60° | Parallel | mm | General fastening | Worldwide |
BSPP/BSPT | ISO 228 / ISO 7-1 | 55° | Both | Inch | Plumbing, fluid systems | UK, Europe, Asia, Australia |
UN / UNF | ANSI/ASME B1.1 | 60° | Parallel | Inch | Fastening (not sealing) | USA, aerospace |
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