... pdc diamond bits Size: 3 7/8"--17" Brand new API&ISO9001:2008 MOQ:1 piece API 8 1/2" 6 Blades New ... applied for rock formations as follows:1. Andesite, marble, metamorphic schist (For hard, low abrasive formations)2. Gneiss, Diorite, Basalt (For hard ... and abrasive formations)3. Quartz, Granite (For very hard ...