... :DTH ,the “down-the-hole” was originally developed to drill large-diameter holes downwards in surface-drilling applications,of which the percussion mechanism followed the bit down into the hole. Applications ... DHD340-105mm,115mm,130mm DHD350R-127mm DHD350Q-130mm DHD360-152mm,165mm,178mm,194mm DHD380-20mm,215mm,216mm,254mm,305mm DHD112-311mm ...