A core bit is a drilling tool with a hole through the center that removes sediment rock and allows the core pedestal to pass through the bit and into the core barrel. The Ocean Drilling Program (ODP) employs different coring systems and bits to obtain continuous cores in all types of oceanic sediments and igneous basement.
Once a coring system is selected based on the expected lithology, the engineer determines which type of core bit to use. As coring conditions change, the coring bit can be changed in an attempt to improve the recovery and rate of penetration with that coring system. The type of bit used depends on the expected lithology and past bit performance in the area or in a similar lithology. Once a bit is removed, it is "graded" (i.e., it is examined to determine wear on the cutting structure, gauge, bearings, etc., based on industry standards) to optimize coring performance.