An engagement mechanism for a driver instrument, the engagement mechanism comprising: a mobile shaft extending along an axis, the mobile shaft comprising: a first shaft portion located at a proximal end of the mobile shaft; a driver portion located at a distal end of the mobile shaft; and an internal passageway extending from the proximal end to the distal end; a collet for coupling to a drive input of the driver instrument, the collet comprising: a second shaft portion disposed within the passageway at the first shaft portion; and flexible arms (232A-232D) extending from the second shaft portion within the driver portion; and an angled engagement interface between the driver portion and the flexible arms configured to permit the driver portion to push the flexible arms radially inward when the first shaft portion is slid along the second shaft portion; wherein the angled engagement interface comprises: a plurality of ramped surfaces (282A-282D) extending from distal ends of the flexible arms to form a frusto-conical shoulder; and a plurality of bearings (224A-224D) mounted to the passageway at the driver portion; wherein the plurality of bearings can be advanced to engage the frusto-conical shoulder to deflect the flexible arms, and wherein the mobile shaft comprises channels (286A-286D) extending into the driver portion within the passageway, the plurality of bearings being located in the channels. a mobile shaft extending along an axis, the mobile shaft comprising: a first shaft portion located at a proximal end of the mobile shaft; a driver portion located at a distal end of the mobile shaft; and an internal passageway extending from the proximal end to the distal end; a first shaft portion located at a proximal end of the mobile shaft; a driver portion located at a distal end of the mobile shaft; and an internal passageway extending from the proximal end to the distal end; a collet for coupling to a drive input of the driver instrument, the collet comprising: a second shaft portion disposed within the passageway at the first shaft portion; and flexible arms (232A-232D) extending from the second shaft portion within the driver portion; and a second shaft portion disposed within the passageway at the first shaft portion; and flexible arms (232A-232D) extending from the second shaft portion within the driver portion; and an angled engagement interface between the driver portion and the flexible arms configured to permit the driver portion to push the flexible arms radially inward when the first shaft portion is slid along the second shaft portion; wherein the angled engagement interface comprises: a plurality of ramped surfaces (282A-282D) extending from distal ends of the flexible arms to form a frusto-conical shoulder; and a plurality of bearings (224A-224D) mounted to the passageway at the driver portion; wherein the plurality of bearings can be advanced to engage the frusto-conical shoulder to deflect the flexible arms, and wherein the mobile shaft comprises channels (286A-286D) extending into the driver portion within the passageway, the plurality of bearings being located in the channels. wherein the angled engagement interface comprises: a plurality of ramped surfaces (282A-282D) extending from distal ends of the flexible arms to form a frusto-conical shoulder; and a plurality of bearings (224A-224D) mounted to the passageway at the driver portion; wherein the plurality of bearings can be advanced to engage the frusto-conical shoulder to deflect the flexible arms, and a plurality of ramped surfaces (282A-282D) extending from distal ends of the flexible arms to form a frusto-conical shoulder; and a plurality of bearings (224A-224D) mounted to the passageway at the driver portion; wherein the plurality of bearings can be advanced to engage the frusto-conical shoulder to deflect the flexible arms, and wherein the mobile shaft comprises channels (286A-286D) extending into the driver portion within the passageway, the plurality of bearings being located in the channels.