Bridge

A bridge is a device for transferring the vibrations of strings to the soundboard in stringed instruments. It raises the strings and separates them to a particular width and is one of the end points of the string as far as vibration is concerned. The other end point is the Nut.

The strings rest on the bridge as they pass over on the way from the tailpiece to the tuning pegs. As the string vibrates, it moves the bridge back and forth very slightly. This rocking flexes the soundboard very slightly which in turn moves the air inside the instrument in the chamber made by the body. This is a rudimentary but effective amplifier. The bridge maybe fixed like on many Guitars (top right) and use pegs to hold Ball End Strings in a combined Tailpiece and bridge or floating like on the Banjo (top right). The height may be adjustable (bottom right). The Bridge bottom left is for a Violin. 

The Bridge has small grooves or depressions filed into it for the strings to sit. Great care should be taken with the profile and depth of the notch to obtain a good sound without buzzing. The same advice pertains for the Nut.