within said housing and operatively connected to the plunger the plunger is connected to the piston means with a first clearance in a plane normal to the direction of the axial movement of the plunger the piston means further is connected to the plunger with a second clearance in the direction of the axis of said drilling unit the drilling unit exhibits excellent linearity of axial motion combined with a high degree of accuracy and at the same time requires as little space as possible in a plane parallel to a plane in which a workpiece is positioned application_number US 46611789 A description as best shown in fig3 a drilling tool 1 is received in a drilling spindle 2 which again is rotatably received within a tubular spindle housing 3 said tubular spindle housing 3 contains an air driven drilling spindle driving motor 12 as indicated by the dashed lines which may be provided in the form of an air driven turbine to which the air is supplied through an air supply line 4 the tubular spindle housing 3 is slideably received within a sleeve like housing 5 consisting of a lower member 5 39 and an upper member 5 34 which are fixed together by means of lugs 6 6 39 connected by screws 7 the lugs 6 at the same time may serve as an abutment to hold the drilling unit as a whole within an opening 8 provided in a carrier plate 9 the housing is.