6.4mm Flex-Hones Aluminum Oxide. Nikasil Applications Hones are made with a softer material, Aluminum Oxide. These special hones are required for todays coated aluminum cylinders. These aluminum oxide hones are recommended for nikasil and chrome coated cylinder bores. The overall tool length is 8". If you cannot find the size and grit desired email us and we can order the hone(s) for you.