I HAVE HUNDREDS OF TIE TACKS, TIE BARS AND CUFF LINKS. tie tack/bar: 1.62" x 0.72" (1-5/8" x 3/4" or 40.5mm x 18mm). collar bar: none. 0.25" = 1/4" or 6mm - pretty small for standard button holes. 0.38" = 3/8" or 9mm - also fits standard button holes.
