Rotary drill bits

A rotary drill bit for connection to a drill string and for drilling boreholes in subsurface formations comprising a bit body having a leading face and a gauge region, a plurality of blades formed on the leading face of the bit and extending outwardly away from the axis of the bit towards the gauge region so as to define between the blades a plurality of fluid channels leading towards the gauge region, a plurality of cutting elements mounted along each blade, and a plurality of nozzles in the bit body for supplying drilling fluid to the channels for cleaning and cooling the cutting elements, wherein there is provided in at least one of said channels, adjacent the gauge region, an opening into an enclosed passage which passes internally through the bit body to an outlet which, in use, communicates with the annulus between the drill string and the wall of the borehole being drilled, the portion of the gauge region outwardly of said opening comprising a bearing surface which, in use bears against the wall of the bore hole and extends across the width of said one channel, thereby to inhibit flow of drilling fluid from said one channel across the gauge region of the drill bit.