In terms of shearing, the thin spot in any DIN connection will be the portion between the DIN threads and the inlet threads. The walls there are thin, the diameter is small and the inlet hole is fairly large to accommodate a filter. Consequentlty whether or not there are 2 threads exposed will make zero difference. Also whether you have 5 threads or 7 threads, a half turn of the wheel is more than enough to get a leak with either, and both are equally likely (or more correctly unlikely) to leak in the event of an impact with the ceiling.
In terms of the 2 extra threads being exposed in a 200 bar valve in salt water, I have a news flash for you - the threads are still exposed to salt water as the connection is not water tight until you reach the o-ring. That is one of the serious faults with the DIN system compared to a yoke. The DIN threads capture and hold more salt water than the fairly open and flat face of a yoke valve. If you are not careful to blow the water out of the valve prior to a fill, there is a much greater chance of blowing some water inside the tank.
Also, unless you rinse the threads in the valve and on your reg, minerals there will dry on the threads themselves. If the threads are "cleaner" when using a 300 bar valve, it just means the threads in the longer 300 bar valve are scraping the crap you should have rinsed off your reg's DIN connection anyway and is more or less evidence that your preventive maintence could be a lot better.
I will periodically (after a week of diving for xample) remove the DIN cap, put my thumb over the hole in the inlet to seal it and rinse the DIN connection threads and scrub them with a toothbrush. I'll also periodically rinse the tank threads and scrub them with a toothbrush as well and then blow any water out of the valve before filliing or storing the tanks.
There is really zero advantage to the 300 bar connection and if anything it just has the potential to trap a bit more water in the valve and also just creates more surface area for salt deposits.
In terms of the 2 extra threads being exposed in a 200 bar valve in salt water, I have a news flash for you - the threads are still exposed to salt water as the connection is not water tight until you reach the o-ring. That is one of the serious faults with the DIN system compared to a yoke. The DIN threads capture and hold more salt water than the fairly open and flat face of a yoke valve. If you are not careful to blow the water out of the valve prior to a fill, there is a much greater chance of blowing some water inside the tank.
Also, unless you rinse the threads in the valve and on your reg, minerals there will dry on the threads themselves. If the threads are "cleaner" when using a 300 bar valve, it just means the threads in the longer 300 bar valve are scraping the crap you should have rinsed off your reg's DIN connection anyway and is more or less evidence that your preventive maintence could be a lot better.
I will periodically (after a week of diving for xample) remove the DIN cap, put my thumb over the hole in the inlet to seal it and rinse the DIN connection threads and scrub them with a toothbrush. I'll also periodically rinse the tank threads and scrub them with a toothbrush as well and then blow any water out of the valve before filliing or storing the tanks.
There is really zero advantage to the 300 bar connection and if anything it just has the potential to trap a bit more water in the valve and also just creates more surface area for salt deposits.
