down the hole drilling Bit for down-the-hole drilling, air reverse circulation drilling. down the hole High Pressure RC Drilling bit Bit for down-the-hole drilling, air reverse ... circulation drilling.Bit Front designs:Complete compatible to be used with DHD hammer DHD330, DHD340, DHD350, DHD360, DHD380, SD18 ... 254mm, 279mm, 305mm, 330mm, 356mm, 381mm, 445mm, 555mm, etc. Down The Hole Drilling Bit