I have only four of these excellent carbon graphite blocks. They measure at least 150mm x 130mm x 9.6mm thick and were made as electrical motor brush material. They are soft, electrically conductive and easy to cut, but messy to work with.
Made by the Pure Carbon Company INC (now Morgan AM&T) in the US, they are high grade materials with lots of uses, such as a heatproof surface, laser absorbtion block, making giant 'lead' pencils, and of course, as electric motor brushes!
Note: only one block has its original wrapping, the others will be supplied in plain paper.