A self-locking, manual surgical instrument designed to force apart two adjacent ribs to permit examination or intervention in the thoracic cavity during a cardiothoracic surgical procedure. It typically has two interchangeable arms/blades at the distal end that hook over the ribs to be parted, and includes various designs to provide a ratchet mechanism to adjust the blades and maintain its set position; it may also be attached to other devices used in the procedure. The device is typically made of metal and is also known as a rib retractor. This is a single-use device.