A rotary-cutter Earth-penetrating bit in which a given track of bottom hole is attacked by inserts of two different types, e.g. chisel-shaped and pointed, wider and narrower, higher and shorter, and/or of different materials. The different types of inserts can both be included within a single row of...http://www.google.es/patents/US6942045?utm_source=gb-gplus-sharePatente US6942045 - Drilling with mixed tooth types
