Instruments for drilling holes for bone screws

An instrument for drilling a hole for a bone screw, the instrument comprising:

• a shaft having:
• a first end;
• a primary drill fluted portion extending from proximate the first end of the shaft toward a second end of the shaft;
• a shank at the second end of the shaft;
• and
• a middle portion between the primary drill fluted portion and the shank, the middle portion having a cross-sectional shape with at least one flat surface;
• a sleeve surrounding the shaft, the sleeve having an inner surface with the same cross-sectional shape as that of the middle portion, which inner surface slides along the middle portion of the shaft;
• a countersink drill bit provided at a first end of the sleeve that is proximate the primary drill fluted portion;
• and
• a locking mechanism that selectively holds the sleeve in a fixed position with respect to the shaft, for locating of the countersink drill bit at a selected position with respect to the first end of the shaft.

An instrument for drilling a hole for a bone screw, the instrument comprising:

• a shaft having an end for drilling the hole, an end for connecting to a drill, and a middle portion between the two ends;
• a sleeve surrounding at least the shaft's middle portion in a longitudinally slidable manner, at least part of an inner surface of the sleeve engaging at least part of an outer surface of the shaft's middle portion in a manner that prevents relative rotation between the sleeve and the shaft;
• a countersink drill bit provided at an end of the sleeve that is proximate the shaft's drilling end;
• and
• a locking mechanism configured to engage with the shaft's middle portion and hold the sleeve in a longitudinally fixed position with respect to the shaft, thereby locating the countersink drill bit at a selected position with respect to the shaft's drilling end.