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Pipe joint thread types are essential for ensuring reliable mechanical connection and sealing in piping systems. Three fundamental parameters define their characteristics:
· Thread Angle: The included angle between adjacent thread flanks.
· Pitch: The axial distance between corresponding points on adjacent threads. Expressed in mm for metric threads or as threads per inch (TPI) for imperial threads.
· Taper: Some threads are tapered to enable self-sealing. Taper is defined by a ratio, such as 1:16, indicating the diameter change over a given length.
Based on function and standards, pipe joint threads are generally categorized into British (BS), American (ANSI), and Metric (ISO) systems. Each system includes both sealing and non-sealing thread types.
Imperial pipe threads, defined by BS 21 and ISO 7/1 standards, feature a 55° thread angle. These are widely used in Europe, Southeast Asia, and plumbing or gas systems globally. Their classification primarily depends on whether the thread provides sealing or not.
American National Standard pipe threads follow ANSI B1.20.1 specifications with a 60° angle. These are prevalent across North America and in sectors like aerospace and heavy machinery due to their robust design for high-pressure environments.
Unlike the 55° angle of British threads, American variants utilize a sharper 60° profile that enhances mechanical strength under pressure but requires precise manufacturing tolerances to ensure leak-free assembly.
"NPT" stands for National Pipe Taper. Both male and female NPT threads are tapered at a rate of 1:16, which means the diameter decreases by 1/16 inch per inch of length. The pitch is expressed in TPI—for instance, NPT 3/4 has 14 TPI.
NPT relies on interference fit via flank deformation to achieve sealing without additional components. It is suitable for high-pressure fuel lines or hydraulic circuits exceeding 30 MPa. Variants like NPTF ("Dryseal") offer even tighter seals without requiring sealant compounds.
NPS stands for National Pipe Straight—cylindrical versions of American pipe threads used where no inherent seal is required from the thread itself. The angle remains at 60°, but there’s no taper involved.
Common subtypes include:
· NPSM: Used for mechanical fastening.
· NPSL: Designed for locking connections via nuts.
· NPSH: Specialized for hose coupling applications using rubber elasticity for sealing.
These find use in detachable joints or temporary installations in low-pressure environments.
Metric pipe threads adhere to ISO standards such as ISO 228 (non-sealing) and ISO 8434 (sealing). They use millimeters as units with a consistent 60° angle across all types.
Metric systems offer simplicity in designation—e.g., M20×1.5 indicates a nominal diameter of 20 mm with a pitch of 1.5 mm—and compatibility across global industrial platforms outside North America or UK-dominated regions.
M-series threads are cylindrical with flat crests/root profiles. They come in coarse-pitch (e.g., M10) or fine-pitch forms (e.g., M10×1). Fit classes include H/g or H/h depending on whether clearance or transition fits are needed.
Used predominantly where threaded joints serve structural rather than fluid-handling purposes—such as mounting ports on valve blocks—they require O-rings or bonded seals to ensure fluid integrity when necessary.
MJ stands for Metric Jack—a specialized metric thread form engineered primarily for aerospace-grade applications demanding high precision under extreme conditions.
MJ modifies standard metric profiles by introducing radiused root contours, reducing stress concentration while maintaining high thread engagement accuracy through strict tolerance control like MJ10×1–4h6h combinations.
MJ threads support high-pressure fluid transfer lines within aircraft hydraulic systems where vibration resistance, minimal leakage risk, and dimensional reliability are critical factors.
JIS standards introduce PT (tapered) equivalent to Rc type British threading but tailored to Japanese equipment dimensions; PF refers to parallel types akin to G series requiring auxiliary seals—commonly seen in plumbing fixtures manufactured in Japan.
DIN standards include:
· DIN2999: A compatible taper thread similar to British R series but tighter tolerance control.
· DIN3852: Applied specifically to compression fittings where metal ferrules create seals without needing gaskets—widely used across German-manufactured industrial machinery.
Correct selection involves evaluating:
· Pressure Rating: High-pressure applications (>10MPa) should use self-sealing types like NPT or Rc+R2.
· Media Characteristics: Corrosive fluids benefit from designs isolating the medium from direct thread contact.
· Assembly Frequency: Frequent disassembly favors straight-thread types like G series that allow easy gasket replacement without damage risk.
By understanding these distinctions among pipe joint thread types—from structural geometry down to application-specific pairing—you can ensure optimal performance across diverse fluid handling scenarios supported by trusted suppliers like FLUIDO, who offer comprehensive solutions including pipe fittings, flanges, valves, and custom-made products tailored to your specific threading needs. Contact FLUIDO
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