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
Aluminium number is 13. Of aluminium isotopes, only one is stable: Al. This is consistent with the fact aluminium's atomic number is odd. It is the only isotope that has existed on Earth in its current form since the creation of the planet. It is essentially the only isotope representing the element on Earth, which makes aluminium a mononuclidic element and practically equates its standard atomic weight to that of the isotope. Such a low standard atomic weight of aluminium has some effects on the properties of the element (see below). All other isotopes are radioactive and could not have survived;