cockring question

Thinking about graduating from a Velcro cockring to metal. Any advice on how to properly measure to get the correct size? JC has some general directions but I’d like people’s experience measuring. Thanks

I've been considering expending my cockring collection, but am nervous that certain colors or designs convey a "coded symbolism"...such as colored handkerchiefs did in the past. A yellow hanky meant "piss play/watersports", Red meant bondage/S&M (I think), etc. Also, where the handkerchief was...