Twofers - 2 bits in each pack. Use course (60 grit) to shape hard materials like stone or cut quickly in softer materials. Regular (100-120 grit) is about right for ceramics and smalti. Medium (170 grit) works well on stained glass. Super fine (600 grit) may be used for dichroic. The 1/8" is for those almost impossible to reach places.