1.Tungsten carbide insert bit, TCI bit, button bit 2.Sizes ... sys 1.Cutting Structure The durability of premium tungsten carbide insert is improved with new formulas and new techniques ... inserts on the gauge surface of the cone, tungsten carbide inserts and hardfacing on the shirttail increases gauge holding capability ... 121, 241, 537….………..………………………………26 131, 211, 537, 517…. tungsten carbide drill bits