I HAVE HUNDREDS OF TIE TACKS, TIE BARS AND CUFF LINKS. tie bar clip/tie tack : none. shirt stud: 0.46" x 0.46" (7/16" x 7/16" or 11.5mm x 11.5mm). collar bar: none. Color: silver. 0.25" = 1/4" or 6mm - pretty small for standard button holes.
eBay