I use PCL, easy to find (Machine Mart), cheap enough, and seem reliable.
My compressor came with a Euro one but the supplier included a PCL one and, as you say, the BSP thread seems common. Whenever I've added to the airtool collection, I've simply bought an extra PCL fitting for it.
There is a 32A version of that connector. I have seen them advertised when looking for 16A ones, probably on Ebay.
They are used by people other than caravanners etc (16A ones inc), you see them in all kinds of places. I've heard/seen them referred to as 'commando' connectors but I've no idea how official that name is.
You can get slightly neater wall mounted units but I agree, they aren't the most attractive connectors.
I started off with PCL, but have decided on Euro for when I put the permanent plumbing around the shed. It's much more common now (even in packs of connectors at Lidl from time to time) and it actually has a larger bore. So I've built up a collection of fittings from said store and am converting my stuff as I use it. As for BSP, it's the standard ISO metric pipe thread :-).
The EN 561 Quick-Action connector that hobbyweld use on their cylinders is leak free (if the O ring is in reasonable condition), however it seems to be rather rare in the UK.
Don't bother with doubled 13A sockets/plugs. without a bit of work, there's no guarantee that they'll actually share the current. As for legality, I think it's 'not specified'! I'm ashamed to say that I've got two 16A commando/BS4343 sockets for the welding circuit on a 20A MCB in the shed. I don't feel at all ashamed about this, due to the fact that we ran an 80 rack data-centre with this arrangement (four sockets per rack, with two independent 20A circuits feeding each pair) for 17 years (still going) and didn't suffer any issues at all. Her Indoors has got a pottery kiln in the garage, that I put on a 32A Commando plug and socket, but that's pretty fixed in position. The 32A or even
63A ones are a bit on the bulky side, the 16A ones aren't really all that bad. I've got them in dado rail trunking (ex-work offices :) along with the 13A sockets, network sockets yada, yada, in the shed and they really don't look out of place.
I was thinking two 13A plugs each with very short say 6" lengths of
1.5mm flex, joined together to a long length of 2.5mm flex.
At small currents I don't doubt that there would be imbalances, but at higher currents, if one fuse was getting a lot more current it would heat up, significantly increasing its resistance - and the short lengths having similar low resistances compared to the fuses, the easy path would then take more current, balancing it up.
You might have to match fuses by experiment, but they are cheap.
That way the 1.5mm cables, the plugs and the individual sockets are each protected by 10A fuses, and the double socket and the 2.5mm cable are protected by two 10A fuses in parallel or 20A.
I'd guess so too. But afaict every individual thing would be in spec.
I'm ashamed to say that I've got [...]
Heh. I've got a 13A plug, some Chinese 20A "BS1363" fuses, and a very thick cable...
I tend to connect it to the cooker socket though, so the only thing which isn't in spec is the socket and plug. And the fuses, of course.
Also I work almost exclusively with thin materials, which probably don't need more than 13A anyway. But I have a new bells 'n whistles TIG welder coming next week..