Someone showed me this object in the hope that I would know what it is. ‘Fraid not. It remains a mystery to me. I considered that it might be a keyring but it’s too thick for that, I think.
It says “Compliments of the Swan pen people” It is hinged so it can fold in half, also it has a spring catch on one of the hinges so it can open up. It’s just over one inch in diameter.
Any ideas about what it might be?
With thanks to Des Bull for photos and information
Goodwriterspens's Blog 
I checked the patent number – it is indeed a keyring, invented by a Mr Leopold Myers, from the same family as the Birmingham steel penmakers of that name. I can e-mail you the pdf of the original patent application if that would be of interest.
Thank you Andy! I suppose it would be fine for large keys but the ones with small holes – Yale locks for instance – might not fit. I know the Myers steel pens well. In fact I have one somewhere. Though they are not held in high regard I admire their simplicity.
Yes, I would like to see the pdf. Very kind of you.
Made between 1907 & 1914 (before M.T & Co became M.T. & Co Ltd)
Thank you, Peter.
A slower response from me due to return to the UK from foreign parts. I have a similar, but different keyring, made by Berkley & Co Td of Birmingham. It is 1 1/2 inches in diameter and belonged to my father, who i think got it at some time in the 1920s, though he too may have inherited it. Modern keys have to be drilled out to pass onto it and it is of traditional, split ring design. The downside is that it does need a screwdriver or similar tool to be inserted into the slot to prise it open. Perhaps this design predates your example which was developed to overcome that problem. I have pictures if anyone wants them, but have no idea how to attach them here. This is my first post.
I would like to see that, David. If you like you can send me a photo at redripple@btinternet.com.