Are there different size bridge pins?
They come in a variety of sizes and shapes, especially when they've been crafted out of different materials, including bone, ivory, rosewood, brass, or plastic. Due to the fact they can be different sizes, you may have to take your guitar and the pins to a luthier to fit them properly into the bridge.
Why are my bridge pins popping out?
Bridge pins tend to pop out when the string's ball end is sitting directly under the bridge pin and not against the side of the bridge pin shank as intended. ... If we take a look at the two diagrams below we can see the guitar string running across the top of the saddle before angling down toward the bridge pinholes.