A down-the-hole drill, usually called DTH is mainly a pneumatic powered rock or ground drill, in which the percussive hammer is located directly behind the drill bit, so the percussion mechanism follows the bit down into the drill hole. The drill pipes transmit the necessary feed force and rotation to the DTH hammer and bit, as well as compressed air for the DTH hammer. Air flushes cuttings up from the bottom of the hole. Drill pipes are added to the top of the drill string as the hole gets deeper. The piston directly strikes the impact surface of the bit, while the hammer casing gives guidance to the drill bit. The fast hammer impact breaks hard rock into small particles, which are blown up by the air exhaust from the DTH hammer.