A pin generally has a only a clutch or screw on backing to keep the pin secured to a button hole. Tie tacs are little different in that they can still be used as a lapel pin but they have a chain with a bar coming off the clutch to go into a shirt button hole. This is what keeps your tie close to your shirt. Using a lapel pin as a tie tac or mis using a tie tac will work but the T bar is better.