On Mon, 25 Aug 2008 09:42:37 -0700 (PDT), Pete C ukdiy
wrote:

Is the thread on a 15mm compression fitting 1/2 inch BSP?

IME almost always yes.

And on a
22mm fitting 3/4 inch?

No unfortunately, would be handy it it was.

Sorry, I should have known that because 22mm and 3/4 inch fittings can
be used together only with special olives, can't they.

A 15mm compression to 1/2 BSP male will have a flat on the threaded
end to seal against a washer.

In a pinch where needing the above, I've used a 15mm compression
coupler and sanded a flat on one side with medium/fine wet'n'dry
paper.

I've got a few 15mm straight couplers so I was hoping to use them,
rather than drive and buy something. The petrol would cost more than
the part! I think in this case, I will get away with a straight
couple.