Why will be the threads G 1/8 and 1/8 NPT offered for pressures and then a nominal pressure range of 400 bar? Where does this limit result from?
Basically, the explanation is very simple: From the certain pressure limit, the thread flanks are no longer ?strong? enough to resist digital pressure gauge of the applied pressure. If pressure gauge octa is too much, there is a risk of shearing for the thread. By the way, the pressure limits come from DIN EN 837-1.
Attention: The maximum pressure up to which a thread can be used depends not only on the thread diameter, but additionally on the selected sealing type and the material of the counter-thread.