Differences between G1/4″ threads

What is the difference between the numerous G 1/4″ threads? And are they compatible among one another? One of my colleagues also often has troubles and gets confused because of all the various G 1/4″ threads which the market has to offer, or which are requested by the customer.
The most common G 1/4″ threads at WIKA are surely the G 1/4 in accordance with EN 837 or DIN 3852-E. But in addition there are many other pressure connections which are all specified as G 1/4″. For example G 1/4 Ermeto and G 1/4 DIN 3852-A, just to name two. Although, as indicated in the designation, all pressure connections have a thread with the nominal diameter G 1/4″, the types of sealing discern so greatly that in some cases a compatibility is not possible.
Thus, G 1/4 per EN 837 is usually metallically sealed, even in front of the thread. A centring cone offers the possibility to also use self-centring seals. However, this thread, which is used for pressure gauge s, requires a blind bore. On the other hand, G 1/4 to DIN 3852-E is widespread in hydraulics. Form E means that behind the thread there is a contact surface with groove, where a standardised plastic flat gasket can be fitted. For diaphragm seal of thread, a simple through-hole with thread is sufficient.
Your contact person will gladly consult you, should you have problems choosing or designating a thread.