Device for fixing a tool on a shaft and machine spindle comprising same

The invention concerns a device for fixing a tool on a shaft, comprising a drawbar which can slide axially inside the shaft and which is used to releasably lock tools fixed on the shaft, in particular for automatically changing tools in automatic machine-tools. The drawbar is housed in the shaft locked in rotation and has an external thread whereon is urged to be pressed a threaded body having a corresponding internal thread. The drawbar is so arranged as to be able to slide in the shaft, by rotation of the threaded body, to enable change of tools.