A tool assembly (20, 120, 220, 320) for use with a surgical tool handpiece (10, 310) coupled to a tool mount (18, 318) having a socket (34, 334) for receiving the tool assembly, comprising: a) a tool holder body (36, 136, 236, 336) having a proximal portion with a proximal end, a distal portion with a distal end, and defining a longitudinal bore extending between the proximal and distal ends (36a, 36b) and defining a longitudinal slot extending through all or a portion of a wall of the tool holder body and in communication with the longitudinal bore, the proximal portion adapted for engagement with the socket (34, 334) of the tool mount, and the bore defining a bore axis; b) a tool shaft (26, 126, 226) having a proximal end and a distal end, the tool shaft extending within the bore and permanently retained relative to the tool holder body (36, 136, 236, 336), and the tool shaft (26, 126, 226) movable about a tool shaft axis (26c, 126c, 226c), the proximal end of the tool shaft having a structure configured to be moved by the surgical tool handpiece (10, 310); c) a medical tool (24, 124, 224) coupled relative to the distal end of the tool shaft, such that movement of the tool shaft (26, 126, 226) results in a corresponding movement of the tool (24, 124, 224), the tool having a length; d) a bearing sleeve retained in the bore and extending around the tool shaft (26, 126, 226), the tool shaft extending within and freely movable relative to the bearing sleeve; and e) a tool guard having a proximal end, a distal end and a central portion, the bearing sleeve disposed in an annular space between the tool guard and the tool shaft (26, 126, 226), the tool guard being a tubular member having a plurality of longitudinally spaced tabs (82, 84) formed in a wall of the tubular member, the tabs (82, 84) being radially deformable into a plurality of configurations with the bearing sleeve and for retentive engagement with the tool holder body (36, 136, 236, 336), and the distal end having an opening sized to permit advancement of the tool (24, 124, 224) therethrough, the tool freely movable relative to the tool guard, wherein relative longitudinal translation of the tool guard relative to the tool holder body (36, 136, 236, 336) longitudinally displaces the distal end of the tool guard relative to the tool holder body and sets a defined working length of the length of the tool (24, 124, 224) extending beyond the distal end of the tool guard, wherein the working length is adapted to be constant while the tool (24, 124, 224) is retained in the socket (34, 334) of the tool mount and wherein the medical tool handpiece (10, 310) drives movement of the tool shaft. a) a tool holder body (36, 136, 236, 336) having a proximal portion with a proximal end, a distal portion with a distal end, and defining a longitudinal bore extending between the proximal and distal ends (36a, 36b) and defining a longitudinal slot extending through all or a portion of a wall of the tool holder body and in communication with the longitudinal bore, the proximal portion adapted for engagement with the socket (34, 334) of the tool mount, and the bore defining a bore axis; b) a tool shaft (26, 126, 226) having a proximal end and a distal end, the tool shaft extending within the bore and permanently retained relative to the tool holder body (36, 136, 236, 336), and the tool shaft (26, 126, 226) movable about a tool shaft axis (26c, 126c, 226c), the proximal end of the tool shaft having a structure configured to be moved by the surgical tool handpiece (10, 310); c) a medical tool (24, 124, 224) coupled relative to the distal end of the tool shaft, such that movement of the tool shaft (26, 126, 226) results in a corresponding movement of the tool (24, 124, 224), the tool having a length; d) a bearing sleeve retained in the bore and extending around the tool shaft (26, 126, 226), the tool shaft extending within and freely movable relative to the bearing sleeve; and e) a tool guard having a proximal end, a distal end and a central portion, the bearing sleeve disposed in an annular space between the tool guard and the tool shaft (26, 126, 226), the tool guard being a tubular member having a plurality of longitudinally spaced tabs (82, 84) formed in a wall of the tubular member, the tabs (82, 84) being radially deformable into a plurality of configurations with the bearing sleeve and for retentive engagement with the tool holder body (36, 136, 236, 336), and the distal end having an opening sized to permit advancement of the tool (24, 124, 224) therethrough, the tool freely movable relative to the tool guard, wherein relative longitudinal translation of the tool guard relative to the tool holder body (36, 136, 236, 336) longitudinally displaces the distal end of the tool guard relative to the tool holder body and sets a defined working length of the length of the tool (24, 124, 224) extending beyond the distal end of the tool guard, wherein the working length is adapted to be constant while the tool (24, 124, 224) is retained in the socket (34, 334) of the tool mount and wherein the medical tool handpiece (10, 310) drives movement of the tool shaft.