... /8"(346mm),14 3/4"(374mm), 15 1/2"(394mm)16"(406mm), 17 1/2"(445mm),18"(457mm), 26"(660mm)Model NO.437,447 ... carbide insert is improved with new formulas and new techniques for insert bit. 2>Gauge Structure Multiple gauge protection with gauge ... receive high WOB in the conventional drilling. It is suitable for various formations by matching cutting structure with different tooth shape ...