... .Sealed Bearing Structure 1.Abrasion resistance and seizure resistance of the bearing are improved and suitable for high rotary speed. 2.The advanced ... new techniques for insert bit.Bearing StructureNon-sealed roller bearing. Drilling fluid can enter the bearing directly for cooling; Balls lock ... /8",4",4 1/2",4 5/8",4 3/4",6",6 1/2",7 1/2",8 1/2",9 1/2",9 5/8",9 7/8",12 1/4",15",15 1/2",17 1/2 ...