On 21/02/2017 20:15, wrote:

extensions look like this but without the nut on:
https://www.raygrahams.com/images/th...038720_188.jpg

I would expect there to be an olive between the nut and the
fitting

which nut and which fitting? I can't imagine how one would get an
olive between the extension piece and the elbow.

That sounds like you have a male - female nipple.
They aren't extension pieces for extending a compression joint.
They have tapered threads and the compression fitting will have parallel
threads.

You need a short bit of pipe and some proper compression or solder
fittings, or do it the easy way and use pushfit.