A 17mm diameter is6¾ in the US & Canada and N in the UK, Ireland, and Australia.
Not traditionally, but if you're broke or if it's a heirloom or you just want to do it that way, go for it. engagement ringA ring given by a man to a woman when they agree to marrywedding ringA ring...
yes if you wont A Purity ring can be whatever you want but most people like the idea of a cross or some kind of inscripting.