Tungsten carbide insert bit, TCI bit, button bit Sizes range from 3 7/8" to 26" . Reliable bearing and lubrication system 1. ... , 537, 517….4 1/2 211, 121, 241, 537….4 3/4 131, 211, 537, 517….5 1/2 131, 211, 537, 517….6 211, 121, 241 ... , 537….17 1/2 131, 211, 537, 517….18 1/2 211, 121, 241, 537….………..………………………………26 131, 211, 537, 517…. 311 tricone bit