Vintage Sterling Black Silver Oval Bracelet N.C.V.

I don’t know anything about this. Purchased a long time ago in an antique store Similar pieces I can be found on the Internet, those say it dates before 1940’s? Please do your own research, I’m not an expert Markings “Sterling 925 Hechon en Mex” N.C.V. In the center Has some tarnish & scratches. Please zoom into pictures to make your own assessment of condition. Clasp works 7” long I don’t know what the center it. Feels light weight. Onyx? Could just be glass, It smooth hard & cool to the touch. Weight shown is approx.