I'm just throwing these up here for future reference to come back to if I ever get around to making my swaybar disconnect.
I like the APIO style and have been playing around with google translate to find some more info on how they actually work.
This is the coupling;

The earlier comments on
this thread had me thinking about ways I could make a pin to get back in. I was surprised to see that this is the couple at full flex;


The pin on the APIO system is long, with a slight taper and a normal cotter pin to lock it in place;


And some clever bugger thought of this to store the pin while wheeling;

There is obviously something inside the coupling to keep it from separating while rotating.
I'm guessing the bigger section is put on the drilled side before a sleeve or end cap is welded on to the end of each section, then the bigger section is pulled back over the sleeves and welded onto the non drilled side to make a fix coupling the can only rotate.
That last bit is just a guess and if I ever get keen to make one for myself I'll make a couple of small tests before cutting a bar from the wreckers.