The tie bar, tie clip, tie clasp or tie slide is an accessory that holds your necktie in place by binding your necktie to the front placket of your shirt.
The tie bar goes between the third and fourth buttons of your dress shirt. It may sound obvious, but a tie bar doesn’t just clip the front end of your necktie to the back end. It fastens both ends to the placket of your shirt.
Finally, never wear a tie bar that’s wider than your necktie. Keep things narrow.