The cutting bit in diamond drilling. It consists of a steel shell containing small cavities in its face and edges into which black diamonds are set. In some types of crown the diamonds can be removed and reset for further use. Grooves, called waterways, are usually provided in the face of the crown to allow the passage of the drilling fluid. For surface-set bits in diamond drilling, it is recommended that 2 to 20 stones per carat should be used in soft ground (such as shale); 10 to 80 stones per carat in medium ground (such as sandstone); and 20 to 150 stones per carat in hard ground (such as granite).