nserts are used when tooth wear becomes the limiting factor in the life of the bit. Both the milled-tooth and insert bits have bearings wear that limits their operating lives. The rock-cutting mechanisms of roller cone bits use a shoveling (gouging) action in soft formations and a crushing (chiseling) action in hard formations. Drag bits are of two types as well: polycrystalline diamond cutters (PDCs) and diamond matrix bodies. The major differences from the roller cone bits are the rock-cutting