Rock drill bits factory Prodrill: R32 thread cross bit, diameter 45-102 mm suitable for drifting and tunneling drilling application, easier to sharpen than X-bits, inset angles are equal on all four sides, Bits 64mm and less are easier to sharpen than button bits of the same size. In certain rock conditions, cross bits tend to produce a spiraled five sided hole (especially in diameters larger than 64 mm).