A kind of thickness gauge, including the transparent measurement pipe for being configured to receive and be slidably connected in the tubulose axle of reverse drill. Tubulose axle has linear graduation line on the surface thereof, for identification the linear measurement used in the thickness in measurement bone bridge gap. Linear graduation line is located at the tubulose axle surface, so as to which at least some linear graduation lines can be observed by transparent measurement pipe. Each linear graduation line, when being aligned when the proximal end with measurement pipe, the linear measurement of the distance between the distal end of measurement pipe and the cutting element of reverse drill is provided, reverse drill is positioned so that center axis thereof is arranged to the longitudinal axis relative to tubulose axle into non-zero angle. Such distance corresponds to the thickness in bone bridge gap.
