Abstract: A tool holder for a gun drill or reamer has internal and external cylindrical rear end pilot portions and a radial pilot flange for precisely connecting coaxially with a rotatable and axially moveable power source. A sleeve confined coaxially within the internal cylindrical portion has an axially extending flat spline surface for effecting driving engagement with a mating flat of a tool shank. A contractible conical split collet at the forward end of the holder coaxially clamps the tool shank when moved axially to a clamping position by means of a non-rotatable nut secured to the collet for cocking out of axial alignment therewith to assure precise coaxial clamping of the tool shaft. The nut is in screw threaded engagement with a rotatable and non-axially moveable collar provided with beveled gear teeth for rotation by a Jacobs type tool.

Abstract: An over-spindle quick-change assembly for releasably securing a tool holding adapter at an operative position with respect to a power rotatable shank spindle comprises a cylindrical sleeve sleeved over the tool holding end of the spindle. A collar rotatable on the sleeve has a threaded portion engageable with a nut on the adapter for screwing the nut and adapter to the operative position, whereat confronting annular surfaces of the nut and spindle end engage each other in sealing relationship. The sleeve is prevented from relative movement on the spindle by a set screw screwed radially into the spindle shank and having a reduced diameter extension confined within a radial hole in the sleeve. The threaded portion of the set screw is dimensioned to prevent its entry into the radial sleeve hole.

Abstract: A power driven rotatable spindle is provided with a conical recess tapering inwardly from one end of the spindle to receive a mating conical shaft of a tool holding adapter at a coaxial operative position whereat the spindle and adapter are splined for rotation as a unit. The adapter is moved axially to and from the operative position by interengageable screw threaded portions of the adapter and collar, which latter is rotatable but not axially movable on the spindle.