Abstract: An automatic draw bar for removably securing machine tools carried by a tool holder within the spindle of a milling machine or the like, in which the tool holder is formed with an internally threaded bore. The spindle is provided with an elongated bore having a recess at its end to receive the shank of the tool holder. A hollow draw bar is slidably carried within the spindle and is exteriorly threaded at one end with a thread engagable with the tool holder interior thread. An elongated draw bar expander slidably carried within the draw bar and responsive to a source of linear power is adapted to couple the threads on the draw bar and tool holder to draw the tool holder into frictional engagement with the spindle upon activation of the power source.