Abstract: A tool bit and holder assembly is disclosed wherein a tool holder having a dove-tailed tang for connection with a mounting tool post is provided with a longitudinal groove in one face thereof; the groove having parallel, longitudinally extending and angularly inclined planar side walls intersecting a planar bottom wall of the groove. A single insert tool bit of trapezoidal cross section, having longitudinally convergent, angularly inclined, planar lateral flanks fits into the tool holder groove with one flank thereof engaging one side wall of the groove. A single wedge member, having angularly inclined and longitudinally divergent planar sides engages the other side wall of the groove and the other lateral flank of the tool bit so that application of force on the wedge to move the same toward the bottom wall of the tool holder groove exerts holding force on the tool bit along three right angularly related axes to securely hold the tool bit in fixed operative position.