Here is a pair of vintage cufflinks, circa 1950. There are sterling silver and hold rectangular shaped stones. The stones look black but also have lines that appear to move with the light as well as the lines you can seen in the pictures. They are marked Ster. Pat 2472958. The patent number dates to 1949. The cufflinks swivel and the swivel seems loose enough that when you hold them on the side and flip them, the stone will hang downwards. The fronts measure 4/5" x 3/5"