The high quality blue ceramic disc is one of the best abrasive discs available on the market! It's less expensive to use than most other discs, and will give great and lasting results. Ceramic (blue) grinding disc, premium: 150 x 6 x 16 mm. For sharpening rakers on 1/4, .325, 3/8, .404 chains with Grindomatic V12, Sematic, & Combimatic. For sharpening 3/4" chains with Combimatic.