Mods, feel free to move this to the appropriate forum if it doesn't fit here.
I was given this brass lens at a watch mart sale awhile ago. There are no markings, and it has a removable cap that looks like a sun lens (not going to test this). The lens does come into good focus when used "straight through" on my F/20 soda straw. I'd compare it to a standard 10mm FL lens based on the image circle it produces. Other than the removable cap, it's one solid piece. The only way to remove the lens would be to unscrew the inner flange.
Modern or vintage, any ideas of a maker? Thanks in advance! Gary