Steel drill bit 1 the taper angle can be 4, 5, 6, 11, 12 degree 2 the drill bit hole Dia. :15~25mm 3 good quality drill bits 2011 Best Steel Drill Bit for Drill Rock (Chiesel Bits)We are the professional supplier for rock drilling machine at high quality and competitive price. We specialize in drill bits, drill rods, DTH hammer, air hose and air compressor for over 10 years.chisel thick blade ...