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 ... on the surface of the cone, tungsten carbide inserts and hardfacing on the shirttail increases gauge ... 537….………..………………………………26 131, 211, 537, 517…. Tungsten carbide insert tooth rock bit