These terrier crystal cuff links are probably circa 1900-1930, based on the “bean” type closure on the back. They are set in an unmarked white metal, which may be silver, or possibly, 800 silver. They polish up with a jewler’s cloth & there does not appear to be a base metal.
The terrier faces are in good shape considering their age & use. The crystals/bezels measure 1/2”, so are slightly smaller than a dime. These cuff links would be a perfect gift for a JR terrier enthusiast.