Abstract: In the disclosed assembly, in accordance with the invention, there is provided a means for preventing drawing-in of air into the housing from ambient atmosphere through the labyrinth seal in the rear lid. The means includes a passage having its inlet communicating with the ambient atmosphere and its outlet communicating with the clearance between the spindle flange and the front lid. The disclosed spindle assembly is primarily intended for use in finishing boring machines wherein the tool spindles are of a flange-type design and are mounted in antifriction bearings. The disclosed spindle assembly prolongs the period of high-accuracy performance of the antifriction bearings and their service life in general.