... .Sizes range from 3 7/8" to 26" , normal sizes consist of 5 7/8", 6", 6 1/2", 7 1/2", 8 1/2", 9 ... 1/2", 9 5/8", 9 7/8", 12 1/4",13 5/8", 14 3/4 ... rubber O-ring sealed bearing or roller non-sealed bearing.4.Used for mining, hydrology, subterranean heat,piling, water well drilling ... customized tools which will decrease the cost of project. 3 7/8''Steel Tooth Bit