I don't think it is a standard grub screw Vince. Feel free to correct me, but the ejector screw has a small round locator on the end that fits into a corresponding hole in the mag housing. The grub screws were brought in as grub screws but were modified at Sterling then phosphated.

Luger fan, thread 7. All Ordnance stores, weaponry, ammunition, clothing etc etc were pooled stores there. So while you started a tour there with NZ commercial Sterlings you could end up with UKicon ones or vice verca. Same as rifles, Australianicon/UK made Land Rovers, Ammunition