There are many unqualified threads found in industry now days especially since the spread of ecommerce. Its important that the threads you use are qualified by industry standards to ensure reliability when in use. Things to look for when purchasing fittings or any threads in that matter are the following;
1. Qualified by certified gauges
2. Produced by quality CNC machining
3. Schamfer on the entry of the thread
4. Substantial wall thickness to give the thread strength
Below is a shot of a recent thread qualification we did before releasing a batch of our brass BSP fittings. As you can see we rejected the below fittings because they did not qualify in the go/no-go area of the thread gauge.