Abstract: A mill is provided for grinding and cutting objects in various wells, such as oil wells, which will typically have a cement plug or a metallic item of debris which must be ground into small enough particles to be circulated out of the hole by circulation fluid pumped through the mill. Helical watercourses have been added to the body of the mill that improves the ability of the circulation fluid to move milled particles beyond the mill. Reverse ports are also provided which divert a portion of the pressurized circulation fluid from the mill interior to the annulus adjacent the mill. The reverse ports are threaded to be closable by a corresponding set screw. An optimized configuration of carbide cutting inserts, attached as part of the mill's grinding tips, is also provided.