Yes, mine's different. There's no sign of any threading and there was no hex socket or slot in the end of the pin before I started drilling. Your comment did make me wonder if there might be a cross drilled pin to lock the main pin in position, but after further thought, I think it unlikely given how tough the pin is to drill. I think my next step will be to find out if it's feasible to remove the remains of the pin by electrical discharge machining, and if so how much it will cost.