Abstract: An extendible tool holder having one end adapted for attachment to the shank of a drill bit and the other end adapted for attachment to a spindle. The tool holder includes an elongate shaft portion having a hexagonal cross-section slideably disposed within a sleeve portion. Each face of the shaft portion has a plurality of ball detent rests in the for of circular indentations therein. The distance of the detent rests from the end of the shaft are different from one another on adjacent faces of the shaft. Staggering the detent rest spacing by deploying the detent rests on adjacent faces of the shaft enables adjustable extension of the tool holder without sacrificing structural integrity. A hollow cylindrical sleeve having ball detents therewithin and a spring-loaded ball detent releasing collet thereupon slides telescopically over the shaft.