Tungsten carbide insert bit ,TCI bit,button bit Sizes range from 3 7/8" to 26" . Reliable bearing and lubrication system. 1.Cutting ... structureThe durability of premium tungsten carbide insert is improved with new formulas and ... , 121, 241, 537….………..………………………………26 131, 211, 537, 517…. Tungsten carbide insert tooth rock bit