These vintage cufflinks were most likely created in the late 1960s, maybe the early 1970s.
They remind me of the Rat Pack and Frank Sinatra. I would totally rock these with a pair of black jeans, and a crisp white shirt, or while wearing a tux.
I love the simplicity of the faceted black Onyx against the diamond-cut finish.
There is a photo that shows measurements and details.