E30 Zone

Just curious as to what this does, or what's behind it?
I can't find any reference to it anywhere.

its a nut its ont he steering rack im sure on my old one i used it to drain the rack out

A nut, really? And yes I do know it's on the steering rack! Actually I think I'd describe it as a bolt, rather than a nut.

I did wonder if it was a drain plug, but I've never seen it mentioned on here to use when someone wants to change their PAS fluid? Would seem an obvious answer though.