Weight on bit Weight on bit Weight on bit (WOB), as expressed in the oil industry, is the amount of downward force exerted on the drill bit and is normally measured in thousands of pounds. Weight on bit is provided by drill collars, which are thick-walled tubular pieces machined from solid bars of steel, usually plain carbon steel but sometimes of nonmagnetic nickel-copper alloy or other nonmagnetic premium alloys. Gravity acts on the large mass of the collars to provide the downward force needed for the bits to efficiently break rock. To accurately control the amount of force applied to the bit, the
Atomic mass or standard atomic weight, by several mass units. Atomic masses expressed in unified atomic mass units (i.e. relative isotopic masses) are always close to whole-number values, but never (except in the case of carbon-12) exactly a whole number, for two reasons: The ratio of atomic mass to mass number (number of nucleons) varies from about 0.99884 for Fe to 1.00782505 for H. Any mass defect due to nuclear binding energy is experimentally a small fraction (less than 1%) of the mass of equal number of free nucleons. When compared to the average mass per nucleon in carbon-12, which is moderately