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Well, in some parts of continental Europe it is and always
has been the right. There doesn’t seem to be any particular reason that the
Christians should have mostly kept this the same as the original. But one
thought is; as the man, facing his bride, reaches straight out with his right
hand (most people are right handed) he naturally touches her left. As she does
his, as now, with more and more men wearing one also, when the rings are
exchanged.

This is a modern practice begun mostly during the second world war, a
consequence of increased numbers of men being separated from their loved ones
and seeking a cheering reminder. This almost happened earlier in history, with
the advent of the gemmal ring, alternatively spelled gimmal or gimmel. This was
two or three decidedly ornamental links, usually with hands and hearts or knots,
fastened together by a hinge, or interlocking like the Olympic... more