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DIN SCUBA Fittings
By Nigel Hewitt

Picture from Kevin at FISHinthecity Most of us are familiar with the A-clamp or International fitting. Originally designed for lower pressures this has been strengthened for up to 232bar of pressure and is widely used. It has certain disadvantages and is being progressively superseded by DIN especially in technical diving circles.
This is a 300bar DIN regulator. Notice that on the A-clamp the O-ring was on the cylinder and is often visible when the regulator is assembled to the tank valve here it is not only on the regulator but it ends up buried inside the system and is hence captive and protected in its working position.
232 bar DIN - 5 thread
Notice 1 inch (25mm) front to back outside dimension and the dimple for the A-clamp's screw. When I bought these they were sold as A-clamps by being supplied with the slug (see below) factory installed. I used them as A-clamps for my first couple of years diving.
If you screw a 300bar DIN regulator in here it winds down the 5 threads and then compresses the O-ring and is ready to dive. Also notice the quite wide but shallow hole at the bottom of the threaded section.
300 bar DIN - 7 thread
Notice 1.4" (35mm) depth and no dimple so an A-clamp frame just will not fit (Yes I know the bull bars are in the way too).
If you screw a 232bar regulator in here it is too deep for the O-ring to tighten against the bottom and it will not seal so there is no danger of blowing your 232bar regs up on 300bar pressure. Also notice that the hole at the bottom of the threaded section is narrower than the 232 bar DIN - what is hard to see in a picture is that it is deeper.
More differences. On the left a 232bar end, notice the diameter of the central piece is larger then the 300bar end on the right. The 300 will fit either. These are regulator inputs coded to prevent a 232bar only fitting being placed on a 300bar tank.
And you remember I pointed out the hole at the back of the DIN pillar valve? Well this is a 300bar DIN filling adapter. It has a tube sticking out that goes into that hole but will not fit the 232bar piller valve. This is done to try and stop you overfilling a tank way beyond its rated pressure.
Between the two systems you can include or exclude any combination of fittings so the two sizes can be used together with safety.
The 232bar DIN slug to screw in and convert DIN to A-clamp. It has a captive DIN O-ring at the other end and this end has one to seat the A-clamp.
If you screw it into a 300bar DIN fitting it just keeps on going down before it seals down and is lost in a hole where the A-clamp cannot reach.
The DIN to A adapter with 1.1" (28mm) max opening, this one's by Apeks.
Um... We don't talk about this one. It's a 300bar DIN to A-clamp converter and I use it for filling at places where I can only get on an A-clamp pump. eg: my club who pump clean air but only 232bar.
It would allow you to put an A-clamp reg on a 300bar tank but if the extra stress broke it we would all say "What a fool. We do hope he's alright" as they drag you off to A+E.
Finally two specials. On the left:
Hands up the guy who said you could probably convert anything. It is a 232 bar tank but a 7 turn 300bar fitting. Put a slug in that and fit an A-clamp.

On the right....
Well... What do you think that is for?