Bridge pin
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Bridge pins are used on some musical instruments to locate the string precisely in the horizontal plane and to affect the sustain of the strings. They are usually made of steel in modern pianos, of brass in harpsichords. The sustain control function of a bridge pin is not needed in modern pianos since the tuning of multiple strings with the same pitch is used to control sustain, however it is crucial to the sustain of harpsichord strings which sound singly.