A machining tool comprising an interchangeable cutting portion and a holder to which said interchangeable cutting portion is adapted to be replaceably mounted; wherein: said interchangeable cutting portion comprises a first part with at least one cutting edge and a second part for connection to said holder, said second part being provided with a conical external abutment surface and an external cylindrical screw thread; said holder is provided with an internal cylindrical screw thread, to which said external screw thread is removably screwed, and a conical internal abutment surface, said conical external abutment surface and said conical internal abutment surface being mutually engageable for positioning the cutting portion and the holder relative to one another; said holder comprising at least one longitudinal passage for a coolant or lubricant fluid; said interchangeable cutting portion comprising at least one duct which, when said interchangeable cutting portion is mounted on said holder, is in fluid communication with said longitudinal passage and in fluid communication with a side surface of said interchangeable cutting portion, near said at least one cutting edge; and characterized in that said holder comprises at least one hole extending from said at least one longitudinal passage to a side surface of the holder, for projecting jets of coolant or lubricant fluid during machining for washing the machining area; and wherein said interchangeable cutting portion comprises a plurality of side holes in fluid communication with said duct and ending in different locations on said side surface of the interchangeable cutting portion near said at least one cutting edge and the duct has an outlet opening on the front end of the first part of the interchangeable cutting portion. said interchangeable cutting portion comprises a first part with at least one cutting edge and a second part for connection to said holder, said second part being provided with a conical external abutment surface and an external cylindrical screw thread; said holder is provided with an internal cylindrical screw thread, to which said external screw thread is removably screwed, and a conical internal abutment surface, said conical external abutment surface and said conical internal abutment surface being mutually engageable for positioning the cutting portion and the holder relative to one another; said holder comprising at least one longitudinal passage for a coolant or lubricant fluid; said interchangeable cutting portion comprising at least one duct which, when said interchangeable cutting portion is mounted on said holder, is in fluid communication with said longitudinal passage and in fluid communication with a side surface of said interchangeable cutting portion, near said at least one cutting edge; and characterized in that said holder comprises at least one hole extending from said at least one longitudinal passage to a side surface of the holder, for projecting jets of coolant or lubricant fluid during machining for washing the machining area; and wherein said interchangeable cutting portion comprises a plurality of side holes in fluid communication with said duct and ending in different locations on said side surface of the interchangeable cutting portion near said at least one cutting edge and the duct has an outlet opening on the front end of the first part of the interchangeable cutting portion.