A non-sterile shaft of metal with a hollow centre designed for overdrilling a surgical screw or screw shaft to expose it for its removal, with another instrument, when the screw head has become defective or detached. The device is commonly called a "hollow mill" or "crown drill", but may also be referred to as a "hollow reamer", and is designed as a cylindrical hollow shell with a thin wall that has saw teeth at the cutting edge. It is inserted into a surgical power tool for rotation. This device may also be used to obtain core bone biopsies. This is a single-use device.