Here's the image you provided, Geoff, with one addition...
[attachimg=#1]
I'm not certain what you mean by, "numbered 3/10 and 90 degrees clockwise and anti clockwise" but I think you mean the "spoke" looking brass at 45-degree increments around the pin.
When I look at this assembly, it appears to have a brass sleeve inserted into the two-piece black plastic, rectangular barrel. The two black plastic pieces are cinched together by the black knob that has a threaded post coming out of it. That's how you can change the distance to the bit or change from DF 500 to DF 700. But I suspect you already knew that...
On the end shown in the image above, you can see a steel sleeve around the pin that has grooves in it. I don't have a tool that spans the pin and engages those grooves but that should be how it is assembled - put a spring in, then the pin, and then screw that sleeve into the brass insert. The arrow above points to a set screw that is threaded into the brass and apparently Loctited in. I suspect that once the steel sleeve is threaded in, they install the set screw to prevent it from backing out and the Loctite to prevent the set screw from backing out.
I also suspect that the "spokes" are anti-rotational features so the brass insert doesn't spin while the steel sleeve is being threaded into it.
Tom