Know anything about 37mm lens sets for iPhone?

Most (if not all) of the camera mounts/holders/rigs for professional and/or semi-pro video production on iPhones and iPads adopted a 37mm screw-in base ring for mounting auxiliary lenses. I'm not sure why: 1) can anyone tell me why (and maybe where the 37mm base started), 2) does anyone know of a manufacturer of lens sets (wide angle, telephoto, and maybe even a zoom), and 3) if anyone doesn't know the answers to the above, but has found and used some lens adapters (i.e., Nikon to 37mm), what would be a good recommendation?

Thanks

Gary