The message
from Harry Bloomfield contains these words:

A ball joint would not be rigid enough, the joint angle would slip with
the lightest pressure. What is needed is one of those joints where it
locks with teeth giving a choice of several fixed angles. That would
need much less pressure on the joint bolt to make it stay where put.

But that's not "infinitely adjustable".

Me, I'd saw a bit of round bar down the middle and weld each half into a
bit of pipe. Cross drill it near one end before sawing and turn it round
so you get room to swing without fouling. File the radius if you're
feeling posh.

--
Skipweasel
Pay no attention to that man behind the curtain.