Abstract Establishes the nomenclature and lays down the leading dimensions to ensure interchangeability within the limits of system A of the following equipment: drill rods and couplings; casings, casing couplings, casing bits, casing shoes, drive shoes and casing ream shells; core barrels, core bits, core lifters and reaming shells. Specifies the characteristics of a range of equipment for drilling holes having diameters from 1.18 in to 7.88 in and yielding cores having diameters from 0.73 in to 6.5 in.