... ISO9001&API best bearing system 20 years history Milled Tooth Rock Roller Bits: 7 7/8 to 14 1/2 ModelTCI ... me a call) .Recommended drilling parameters of tri-cone rock bits Rock formationBit typeBit sizeDrilling weightRotary speedmminchkN/mmr/minVery softSoft Marl, Clays ... -9 1/2539-83360-40medium hardHard Dolomite, Limestone, Hard Sandy, Rock etc.595.2~174.63 3/4-6 7/8294 ...