Our HDD drill bits are designed to easily penetrate granite. Progress begins at the HDD bit. HDD rock bits are roller cone or tri-cone with internal bearings to allow the bit to move freely. The cutting edges of the bit are hundreds of contact surfaces turning at varied revolutions per minute with varied amount of pressure or weight put on the drill string. Water and a mixture of inert clay is circulated through the bit to lubricate the drill pipe, cool the bit and lift rock samples to the surface.