... symmetric drilling tools, eccentric drilling tools, standardized API system casings, bit shanks and casing tubes which are ... unique competence in drilling technology. An integrated production system has been formed in the workshops, and the ... Tapered Drill BitType --Chisel Bits / Cross Bits / Button Bits Diameter---28mm,30mm 32mm,34mm,36mm,40mm,42mm ... /H22, Diameter---20mm - 42mm. T51 Thread button bits