The gear was used in Sony CD changers produced in the mid to late 1990s. It is a part of the CD tray and is responsible for the CD tray rotating.
Faulty gear can be replaced with 3D printed one.
Video showing replacement gear in operation.
Gear is compatible with following devices: CDP-C23, CDP-C235, CDP-C245, CDP-C265, CDP-C345, CDP-C435, CDP-C445, CDP-C545, CDP-C661, CDP-C745, CDP-CA9ES, CDP-CE335, CDP-CE415, CDP-C250Z, CDP-CA8ES, CDP-CE525. However, it might work also with other devices – just check your service manual.