Stainless Steel Threaded Fittings. Why Use These in the Plants?

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threaded fittings

Strength, reliability over time, hygiene and corrosion resistance are the basic characteristics for a plant in many installation area. Stainless steel threaded fittings are the ideal solution in these cases.

What are fittings and where can we find them?


There are kilometers and kilometers of piping systems in every city, although not always visible.

These are used to transport different types of solid, liquid or gaseous materials. The most common materials are water and combustible gas. Each piping system consists of pipes and fittings. The latter serve precisely to close or join multiple pipes (even of different diameters). There are different types of fittings on the market, many also with thread.


Threaded fittings: what is threading?


First, there are two types of threads:

  • “not tight on the thread” (according to ISO 228-1 standard)
  • “tightly on the thread” (according to EN 10226-1 standard).

In both cases, the nominal diameter is conventional and it is referred to the theoretical internal diameter of the pipe on which the thread is used.


Types of threads: let’s examine each of them in more detail!




As mentioned above, this type of threads are compliant with the ISO 228-1 standard. But why are they called “not tight on the thread”? The reason is simple, the male thread is cylindrical as well as the female thread. The grip, therefore, is not generated by friction between the two threads. In conclusion, with this type of threads, it is necessary to use a sealing material (e.g. flat packing ring) to prevent fluid leakage from the junction. In addition, according to the UNI 7129-1 standard (standard for threaded gas systems), the use of this type of terminal thread is not allowed in the case of gas-vehicle systems.




Threadings that comply with the EN 10226-1 standard, on the other hand, are defined as “tightly on the thread”. In this case, the male thread is conical, while the female thread is cylindrical. The grip, therefore, can take place directly on the thread. Although in this case it isn’t necessary, sealant material is often used to prevent any leakage. Therefore, stainless steel fittings with threading in accordance with EN10266 / ISO7 standard  (that allow watertight couplings) are perfectly suited to the construction of fuel gas distribution plants (according to EN1775 and UNI 7129 standards).

For example, our fittings are characterized by the austenitic stainless steel AISI 316.

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