Tony:
Thank you. I'm eternally grateful and will press in a bent piece of copper pipe fitted with a rubber cap until the day I find an original wee willie thingie!
Your photo blown up to full scale gave me the size and angle perfectly. Would you believe there are seven other CMPs in the yard and not one other has a compressor so I could compare!
I also posted the question on another forum. For the education of those who don't do both, I have posted your picture and an explanation there.
Amazing thing (not Thing) this internet...!
Mike