... a professional productions base of series of rock drilling tools, mining tools, DTH Drill tools. Construction tools and excavating coal pick ... standard hex. Bit diameters include 20-42mm. 2. Tapered drilling tools (Tapered Drill Steel)Including:Shank H22x 108mm, (6, 7, 11, ... , 12 degree taper).Bit diameter: 28mm-57mm. 3. Extension drilling toolsButton bit, face design: Flat face, Drop centre, Normal ...