This is a bridge adjuster for a double bass. It is a new, unused stock item. Set of 2. Both the embedded side and the screws are made of brass. Commercially available ones are often made of silver-colored aluminum, but aluminum has a lighter specific gravity and is softer, so the response is slightly duller. (I believe this is the reason for the common belief that adding an adjuster makes the sound worse.) Brass has a more solid feel, a longer sustain, and a more natural sound. It should fit without any problems on the bridge of a general 4/4 or 3/4 size instrument. The processing requires the skill of a craftsman, so please take it to a local workshop.