This item belonged to my father, who enjoyed making guitars in his lifetime. It's a plate used to evenly apply pressure and prevent slippage when gluing the X-bracing bridge plate. I believe it's made of resin or something similar. Even if glue gets on it, it comes off easily. My father always emphasized that the bridge plate not only needs to be firmly glued to the top wood but also needs to be in close contact with the high and low-frequency bracing to change the sound transmission. This plate is useful for preventing slight shifts when directly clamping the bridge plate, as the clamping force (which isn't just downward but also sideways) can cause it to move. It's also helpful when attaching the bridge itself, allowing you to clamp it without interfering with the bracing. There are signs of use and old scratches. Please consider this a used item before purchasing. Guitar Repair Handmade Guitar Woodworking DIY Martin Gibson Merrill Santa Cruz Vintage Guitar