I did the same as you, Steve, and used my calipers to measure the hex. 28 mm was too small.
Thanks guys. I tried 1-1/8" - too small. 1-1/4" too big! ....
I'm afraid that if I get it off with an adjustable spanner I may chew it up up even more and won't be able to tighten it enough to stop it leaking when I put it back.
AJ
Thanks guys ! I purchased a new one from Moss but size seemed too large. I kept my old one and will try heating up like Steve suggested !