Abstract: An apparatus and method for securely, mechanically retaining an elongated tool holding arbor in the tapered bore formed in the spindle of a conventional, rotatable, power driven spindle machine. The arbor is mechanically secured to the spindle by bridging it to a key via a threaded fastener. The arbor includes a longitudinal hole formed therethrough having at least first and second concentric passageways of different diameters. The rectangularly shaped key is sized to be operatively received within and set upon shoulders formed by first and second diametrically opposed openings formed through the spindle. The key includes a tapped hole formed centrally, transversely therethrough. The arbor may be inserted into the spindle's bore, and a fastener having an enlarged head and a threaded shaft may be inserted through the arbor's hole with the threaded shaft passing freely through both first and second passageways, and the head passing through the first passageway but not the second.