Abstract: A core tool comprises a pair of partial circles made from suitable material, such as cold rolled steel, with corresponding adjusting means. The adjusting means may be two threaded screws with a center nut, wherein one of the threads is a left hand thread, and the other is a right hand thread. A reversible ratchet or wrench can be used to open and close the circles. Alternatively, the adjusting means could be an air or hydraulic system capable of opening and closing the circle portions. Each pair of partial circles forms a circular diameter that will fit inside a standard core, or multiple core sizes. The core tool, formed of the pair of half circles and the tightening and expanding means, is insertable into a damaged core to reshape the core into its intended circular dimension.