How do I fix a buzzing bridge pin?

Good news: this is one of the easier buzzes to diagnose, because bridge pins are simple objects with a small number of ways to fail.

What's actually happening

A bridge pin's job is to hold the ball end of the string firmly against the bridge plate inside the guitar. When a pin buzzes, it's usually because it isn't seated fully, isn't making solid contact with the string ball end, or has worn down enough to rattle slightly in its hole under vibration.

The usual suspects

• Pin not fully seated. Pull it, check the slot lines up with the string's ball end (the slot should face the fretboard, roughly), and reseat firmly.
• Worn or mismatched pins. Plastic pins wear over time, and cheap replacement sets aren't always cut to the same taper as your bridge holes. A loose-fitting pin will rattle.
• String ball end sitting wrong. If the ball end has slipped past the pin instead of being pulled snug against it, you'll get buzz or even a string that pops loose under tension.
• A worn or oversized pin hole. Less common, but if the bridge itself has worn or was drilled loose, pins won't seat with enough friction no matter what you do.

The fix, roughly

Restring properly — ball end seated against the pin, pin pushed down firmly while you bring the string to tension, slot facing the neck. If that doesn't solve it, the pins themselves (or the holes) may need attention. Bone or fitted pins solve a lot of the "cheap plastic pin rattle" problem outright.

If you've reseated everything and it's still buzzing, there might be more going on with the bridge plate itself. Worth a look before you keep guessing.