The Channel Disc™ brand disc has a uniquely shaped working surface of randommly interspaced islands. The resulting channels flush away debris and prevent the stone from pulling down excessively to the lap. It is superb for rough cutting facets and grinding cabochon backs. Note: Channel Disc™ brand discs will cut faster and coarser than standard discs. 180 mesh is an excellent cabochon preformer - 360 mesh is superb for facet roughing - 1200 mesh is excellent for facet finishing. 1/2" Arbor hole.