The following article was sourced from a Wikipedia page at the following address: http://en.wikipedia.org/wiki/Collar_pin
A collar pin (closely related to the collar bar and collar clip) is a piece of men's jewellery, which holds the two ends of a dress shirt collar together and passes underneath the knot of a necktie. Functioning in a similar way as a tabbed collar, it keeps the collar in place and lifts the knot to provide a more aesthetically pleasing arc to the necktie.
A collar pin is between three and five centimetres in length and is one of three kinds:
The latter two styles do not require specially made collars, but collar bars are generally not worn with buttoned-down ("polo") collars and would be redundant with tabbed collars. Collar stays are not needed when using a collar bar. As a general matter, collar pins work best with straight, minimally spread collars; least, if at all, with spread collars; and not at all with widely spread collars such as the cutaway.
To read more about collar pins, please click on the following link: http://en.wikipedia.org/wiki/Collar_pin