Do you know about the metric thread identification process? from boschhydraulic's blog

Metric threads. This a term that you might have heard if you are someone who belongs to a mechanical background. Even if you aren’t, you might have had an interest in this domain. If this is not true, then also it’s alright. Get ready to learn something new. The term “Metric thread” comes up when there is a discussion about Metric Adapters. For any kind of hydraulics system to function properly, it needs the right kind of adapters. These are parts that join different systems together which cannot be joined directly. For identification, check whether the threads are parallel or tapered. Next, you need to check the pitch by using a vernier calliper. The measurement unit will be in millimetres. Again, use the callipers to identify the outside thread diameter. After all, the measurements are done, use them and compare them for identification and choose which thread suits your purpose. There are more than 15 threads that one needs to choose from. A proper comparison needs to be done.