Understanding metric threaded ports for fittings can be tricky, but let’s make it simpler. There are two main types you’ll hear about: ISO 6149-1 and DIN 3852-1 (which is the same as ISO 9974-1).
Here’s the key difference:
ISO 6149-1 Port:
This one has a special area near the top of the threads where an O-ring fits. Think of an O-ring as a small rubber ring that helps prevent leaks.
DIN 3852-1 / ISO 9974-1 Port:
This style is different because the threads go all the way to the top of the port, with no special area for an O-ring.
Even though both types use metric threads (the way the threads are measured and shaped) and usually have the same thread size and pitch (how close the threads are to each other) for a specific fitting size, they are not the same. That’s what often causes confusion.
Conclusion
In short, the main thing to remember is that ISO 6149-1 has a special spot for an O-ring at the top, while DIN 3852-1 / ISO 9974-1 does not.
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