Never mind, it's a trivial turning milling and tapping exercise. 9 mm pin, two flats to mill and an axial 6 mm hole to tap. Needs to be a bit more than mild steel so I decided to turn down a 16 mm HT bolt as I had a box of them. I also decided to turn it in the hard and tempered state rather than soften, turn and re-harden and temper, as carbide tooling easily deals with HT.
As it was going to be rather long sticking out of the chuck I used a 'rotating' centre. First time I'd used this particular one, and I chose it for its relatively thin nose section to allow better access at that end of the turn.
Fitted, adjusted the tail stock, checked it was freely rotating and started reducing the bolt from 16 mm to 9 mm . Initially a nice finish but then, hang on, why's the finish so awful?
Turns out that the bearing in the rotating centre has seized and melted the tip off the centre!