Bridge pins are used on some musical instruments to locate the string precisely in the horizontal plane, and in the case of harpsichords to affect the sustain

Sustain

In music, sustain is a parameter of musical sound over time. As its name implies, it denotes the period of time during which the sound remains before it becomes inaudible, or silent.Additionally, sustain is the third of the four segments in an ADSR envelope...

 of the strings. They are usually made of steel in modern piano

Piano

The piano is a musical instrument played by means of a keyboard. It is one of the most popular instruments in the world. Widely used in classical and jazz music for solo performances, ensemble use, chamber music and accompaniment, the piano is also very popular as an aid to composing and rehearsal...

s, of brass in harpsichord

Harpsichord

A harpsichord is a musical instrument played by means of a keyboard. It produces sound by plucking a string when a key is pressed.In the narrow sense, "harpsichord" designates only the large wing-shaped instruments in which the strings are perpendicular to the keyboard...

s, and bone or synthetics on acoustic guitars. Electric guitars do not usually have bridge pins as, in guitars, they are used to transfer the sound from the strings into the hollow body of the instrument as well as holding the strings in place.

In pianos the pins are set precisely in line with the edges of the notches of the bridge. The precise and firm setting of the pins is a critical element of the piano's quality. Loose or inaccurate pinning commonly produces false beats and tonal irregularities.

In harpsichords there tends to be a significant distance instead. This enables
control of sustain and tone in harpsichord design (as per external link).

Bridge pin may also refer to:

• Bridge pin (fasteners), a device for fixing clevis or hitch pins.