Right, you buy a brand new head for nigh on £1000 and the 98p threads that close off the oil galleries (little black thread with allen key hex hole) don't come with it

I have managed to recover all but one off my old head (missing a large one at the back on the head). I have ordered one, but, want to make sure I have a backup plan if it doesn't turn up on time so that the car can make it to the pod.

Are there alternatives readily available, it looks like an M10 size thread, but the thread itself is much closer than an M10 bolt if you see what I mean.

I am open to ANY suggestions...

PS: of secondary interest, why are those holes there in the first place ?