**Main Types of Pipe Threads:** Pipe threads are primarily categorized as follows, each with distinct characteristics and designations:
**55° British Non-Sealing Pipe Thread (G):** Designated by the code "G," this type is used for mechanical connections and does not provide a seal on its own; sealing relies on components like gaskets. Both the internal and external threads are cylindrical.
**55° British Sealing Pipe Thread:**
**R** (formerly ZG): Tapered external thread.
**Rc:** Tapered internal thread.
**Rp:** Cylindrical internal thread. Sealing pipe threads achieve a tight fit via thread taper (1:16) and possess inherent sealing capabilities; however, fillers such as PTFE tape or sealant are usually required to ensure a reliable seal. Common mating combinations include Rc/R (taper/taper) and Rp/R (cylindrical/taper). **60° American General-Purpose Sealing Pipe Thread (NPT):** An American standard with a 60° thread angle and a taper. Designated as "NPT," it is commonly used in North America. 💡 **Guidelines for Pipe Thread Selection and Use**
1. **Consider Sealing Requirements:** Determine whether the connection must withstand pressure. Non-sealing pipe threads (G series) are suitable only for mechanical connections in non-pressurized applications and must not be used for pressure-tight sealing.
2. **Distinguish Thread Types:** Always verify thread designations (G, R, Rc, NPT, etc.) during procurement or installation; threads from different standards systems are not interchangeable. In the old Chinese national standard, ZG corresponds to the current R (tapered external thread).
3. **Consider Pressure Ratings:** For sealing pipe threads, material and machining precision affect pressure-bearing capacity; select threads based on the system's design pressure.
4. **Use of Fillers:** Even with sealing pipe threads, actual installation usually requires fillers-such as PTFE tape or sealant-to fill microscopic irregularities and ensure a reliable seal.
5. **Material Compatibility:** In special operating conditions (e.g., involving corrosive media), consider the compatibility of the threaded component's material with the fluid and the external environment. 6. Machining and Inspection: Machining precision requirements for pressure-tight pipe threads are higher than those for non-pressure-tight pipe threads. The accuracy of the taper and thread profile angle is critical to sealing performance. 📝 Important Note
The data in the table is primarily derived from national standards; however, slight discrepancies in specific values may exist across different versions of standards or reference materials. For critical applications, always consult and adhere to the latest national standards (such as GB/T 7306.1-2000, GB/T 7306.2-2000, GB/T 7307-2001, GB/T 12716-2011, etc.) or relevant industry specifications.
"Colloquial terms" (such as "4-fen" or "6-fen") originate from Imperial units (where 1 inch = 8 "fen"). However, in professional practice, it is strongly recommended to use size designations (e.g., 1/2 inch) or nominal diameter (DN) ratings (e.g., DN15) for communication and verification to avoid ambiguity.
The "nominal diameter" (DN) of a pipe thread refers to the nominal bore of the pipe it connects, not to any specific diameter dimension of the thread itself; consequently, the actual dimensions of the thread will exceed the nominal diameter.
