I HAVE HUNDREDS OF TIE TACKS, TIE BARS AND CUFF LINKS. cuff links: 0.85" x 0.79" (7/8" x 13/16" or 21mm x 19.5mm). I always try to point out any clear blemishes and condition. Color: gold, black. 0.25" = 1/4" or 6mm - pretty small for standard button holes.
