Rotary drill bits for use in coring holes in subsurface formations

A rotary drill bit for use in coring holes in subsurface formations, comprising a bit body having a shank for connection to a core barrel, an outer peripheral gauge portion for engagement with the peripheral wall of the hole being drilled, an inner peripheral gauge portion defining at least a part of a central, generally circular aperture extending axially through the bit body, a plurality of cutting elements mounted at an end face of the bit body, at least one passage in the bit body for delivering drilling fluid to said end face of the bit body for cooling and cleaning said cutting elements, and sealing means on said inner gauge portion of the bit including an annular resilient member received in an annular groove in the inner gauge portion of the bit body, the annular resilient member being formed from resilient material and having a plurality of axially spaced annular recesses in the inwardly facing surface thereof so as to define, between the recesses, a plurality of inwardly projecting resilient annular flanges, the inner peripheries of which, in use of the bit, engages the outer peripheral surface of the core being cut by the bit in a manner to form an hydraulic seal and prevent or restrict flow of drilling fluid in an axial direction between the inner gauge portion and the core.